KR20230155274A - Method for bond trading on blockchain and apparatus for performing the method - Google Patents

Abstract

The present invention relates to a bond trading method on a blockchain and a device for performing this method. The bond trading method on the blockchain involves the steps of a bond issuing node transmitting a bond issuance request transaction to the blockchain, a bond listing node deciding whether to list a bond based on the bond issuance request transaction, and sending the tokenized bond to a bond trading node. It may include a step of transmitting to and a bond trading node providing trading services for tokenized bonds.

Description

Method for bond trading on blockchain and apparatus for performing the method}

The present invention relates to a bond trading method on a blockchain and a device for performing this method. It relates to a bond trading method on a blockchain for trading digitized bonds on a blockchain and a device for performing this method.

Blockchain refers to a digital ledger that encrypts transaction information that occurs in a public network or private network and then shares it among network members.

In blockchain, a copy of the transaction ledger is distributed and stored to each network member, and whenever a new transaction occurs, a transaction authentication procedure is performed according to the consent of the members. Therefore, in blockchain, transaction information cannot be arbitrarily changed.

During blockchain-based transactions, transaction reliability increases and information tracking is easy. In particular, when blockchain technology is applied in the financial services field, work efficiency can increase and new services can be established.

When applying blockchain to financial services, it is possible to reduce security, supervision, and regulatory costs through transparent transactions using distributed ledgers. Blockchain technology can be applied not only to the financial sector but also to logistics, distribution, and government public administration services.

Since the process of depositing and transferring money in the digital bond market itself must be performed by each user in the payment system, there is a problem in that the depository must record the transfer details one by one. In other words, there is a problem where the depository has to enter the numbers corresponding to the transfer details one by one. Therefore, research on blockchain-based bond trading technology is necessary.

The purpose of the present invention is to solve all of the above-mentioned problems.

In addition, the purpose of the present invention is to enable buyers and sellers to trade tokenized bonds through bond transactions on a blockchain and to transparently monitor bonds.

In addition, the purpose of the present invention is to enable cancellation before the transaction is made on the block when making a decision about an abnormal transaction and when making a transaction on a blockchain.

In addition, for bonds where issued funds such as ESG bonds are used for projects that create eco-friendly or social benefits, the status of fund use is confirmed through the blockchain system, sharing indicators showing the impact, and further utilizing token incentives for investors. The purpose is to enable monitoring.

A representative configuration of the present invention to achieve the above object is as follows.

According to one embodiment of the present invention, the bond trading method on the blockchain includes the steps of a bond issuing node transmitting a bond issuance request transaction on the blockchain, and a bond listing node determining whether to list the bond based on the bond issuance request transaction. It may include transmitting the tokenized bond to a bond trading node and providing a trading service for the tokenized bond by the bond trading node.

Meanwhile, the transaction service is performed based on a trader node (sell) and a trader node (buy), and transactions for the tokenized bond based on the transaction service can be recorded on the blockchain.

In addition, the bond monitoring device further includes a step of recording monitoring information about the tokenized bond on the blockchain, wherein the monitoring information may include quantitative indicators for the tokenized bond and issuer post-report evaluation data. You can.

According to another embodiment of the present invention, a blockchain bond trading system for bond trading on a blockchain includes a bond issuance node implemented to transmit a bond issuance request transaction on a blockchain, and whether or not a bond is listed based on the bond issuance request transaction. It may include a bond listing node implemented to determine and transmit the tokenized bond to a bond trading node and a bond trading node implemented to provide a trading service for the tokenized bond.

Meanwhile, the transaction service is performed based on a trader node (sell) and a trader node (buy), and transactions for the tokenized bond based on the transaction service can be recorded on the blockchain.

In addition, it further includes a bond monitoring device to record monitoring information about the tokenized bond on the blockchain, and the monitoring information may include quantitative indicators for the tokenized bond and issuer post-report evaluation data. .

According to the present invention, tokenized bonds can be traded by buyers and sellers through bond transactions on the blockchain, and bond monitoring can be performed transparently.

In addition, according to the present invention, the purpose is to enable determination of abnormal transactions when conducting transactions on a blockchain, and to enable cancellation before transactions are made on the block when determining abnormal transactions.

In addition, for bonds where issued funds such as ESG bonds are used for projects that create eco-friendly or social benefits, it is possible to check the status of fund use through the blockchain system and share indicators showing the impact, and furthermore, tokens. Monitoring of investors is possible using incentives.

Figure 1 is a conceptual diagram showing a blockchain bond trading system according to an embodiment of the present invention.
Figure 2 is a conceptual diagram showing a method of trading tokenized bonds in an embodiment of the present invention.
Figure 3 is a conceptual diagram showing a monitoring method for tokenized bonds according to an embodiment of the present invention.
Figure 4 is a conceptual diagram showing a method of trading tokenized bonds on a blockchain according to an embodiment of the present invention.
Figure 5 is a conceptual diagram showing a bond trading method according to an embodiment of the present invention.
Figure 6 is a conceptual diagram showing a bond trading method according to an embodiment of the present invention.
Figure 7 is a conceptual diagram showing a bond fragmentation trading method according to an embodiment of the present invention.

The detailed description of the present invention described below refers to the accompanying drawings, which show by way of example specific embodiments in which the present invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It should be understood that the various embodiments of the present invention are different from one another but are not necessarily mutually exclusive. For example, specific shapes, structures and characteristics described herein may be implemented with changes from one embodiment to another without departing from the spirit and scope of the invention. Additionally, it should be understood that the location or arrangement of individual components within each embodiment may be changed without departing from the spirit and scope of the present invention. Accordingly, the detailed description described below is not intended to be limited, and the scope of the present invention should be taken to encompass the scope claimed by the claims and all equivalents thereof. Like reference numbers in the drawings indicate identical or similar elements throughout various aspects.

Hereinafter, several preferred embodiments of the present invention will be described in detail with reference to the attached drawings in order to enable those skilled in the art to easily practice the present invention.

Figure 1 is a conceptual diagram showing a blockchain bond trading system according to an embodiment of the present invention.

In Figure 1, a blockchain bond trading system for issuing bonds and trading bonds based on blockchain is disclosed.

Referring to Figure 1, the blockchain bond trading system may include a bond issuing node 110, a bond listing node 120, a bond trading node 130, a trader node 140, and a bond monitoring node 150. .

The bond issuing node 110 may be a node that wishes to issue a bond. The bond issuance node 110 may transmit a bond issuance request transaction on the blockchain or directly to the bond listing node 120.

When requesting a bond issuance, the bond issuance node 110 may transmit bond information requesting issuance through a bond issuance request transaction. Bond information includes type of bond (bank bond, power generation company, public bond, corporate bond, government bond, etc.), bond issuance date, bond issuance amount, bond maturity, issuance interest rate (bidding, book-building or issuer's proposed interest rate), bond rating (credit rating agency) ) may include information such as. The bond issuance request transaction may be transmitted to the bond listing node 120 through the blockchain.

The bond listing node 120 may be implemented to determine whether to list bonds so that bonds can be traded, tokenize the bonds determined to be listed, and deliver them to the bond trading node 130.

The bond listing node 120 determines whether to list the bond after reviewing whether it is registered with the exchange and related financial institutions (KCGS, etc.), and records a smart contract for listing and trading the bond on the blockchain.

Additionally, the bond trading node 130 may be implemented for trading tokenized bonds. The bond trading node 130 can receive a bond subscription transaction and deliver the bond to the trader node 140 based on a smart contract.

The trader node 140 allows nodes of whitelisted participants (security firms/related financial institutions/investors, etc.) with completed KYC to transmit bond subscription transactions for bond amount payment, private key signature, contract consent, and subscription based on the corresponding smart contract. You can. The KYC information of the trader node 140 is encrypted and recorded to verify whether KYC has been completed, and other information may not be exposed.

Tokenized bonds may be sent to the wallet of the trader node 140 based on the subscription transaction by the trader node 140. The bond may have an NFT format with a serial number assigned to it.

When a bond is delivered to the trader node 140, the amount paid to the smart contract based on the bond subscription transaction can be sent to the wallet address of the bond issuing node 110.

The bond monitoring node 150 may be implemented to monitor tokenized bonds. The bond monitoring node 150 can monitor the transaction history of tokenized bonds based on the wallet address of each node (bond issuing node, bond trading node, trader node).

Additionally, the bond monitoring node 150 may perform bond issuance impact assessment monitoring. A bond issue impact assessment can be monitoring of environmental and social effects.

The bond monitoring node (150) checks whether or not bonds are disclosed (once a year until the entire issued fund is distributed) and compares the average impact value compared to the bond support amount for companies using the same impact quantitative indicator under the same evaluation grade and criteria (yearly). ) and rankings (e.g., environment: CO2 reduction amount, society: loan amount, number of supported companies, number of employment increases, etc.) can be monitored.

That is, according to an embodiment of the present invention, the bond trading method on the blockchain includes the steps of a bond issuing node transmitting a bond issuance request transaction to the blockchain, and a bond listing node determining whether to list a bond based on the bond issuance request transaction. It may include transmitting the tokenized bond to a bond trading node and providing a trading service for the tokenized bond by the bond trading node.

The trading service is performed based on trader nodes (sell) and trader nodes (buy), and transactions for the tokenized bonds based on the trade service can be recorded on the blockchain. The bond monitoring device further includes a step of recording monitoring information about the tokenized bond on the blockchain, but the monitoring information may include quantitative indicators about the tokenized bond and issuer post-report evaluation data.

Figure 2 is a conceptual diagram showing a method of trading tokenized bonds in an embodiment of the present invention.

In Figure 2, a method of trading tokenized bonds based on blockchain is disclosed.

Referring to FIG. 2, bond trading between trader nodes 210 and 220 may occur on the bond trading node 200.

A trader node (sell) 210 who wishes to sell a tokenized bond may transmit a bond sale transaction including transaction condition information for the tokenized bond to the bond trading node 200. The trader node (buy) 220 can request a transaction for tokenized bonds based on transaction condition information. The trader node (buy) 220 may create a bond purchase transaction along with the transaction amount upon a transaction request based on the transaction condition information and transmit it to the trader node (sell) 210.

The bond trading node 200 can receive bond purchase transactions and bond sale transactions and proceed with bond transactions based on smart contracts for trading.

When a bond transaction based on a smart contract is established, tokenized bonds stored in the wallet of the trader node (sell) 210 may be delivered to the wallet of the trader node (buy) 220.

The bond transaction node 200 can disclose bond transactions by providing bond transaction records stored on the blockchain.

In addition, the bond trading node 200 can pay interest and principal related to bonds generated based on bond information to the wallet of the trader node holding tokenized bonds based on a smart contract for repayment of principal. there is.

Figure 3 is a conceptual diagram showing a monitoring method for tokenized bonds according to an embodiment of the present invention.

In Figure 3, a method by which a bond monitoring node performs bond-related monitoring is disclosed.

Referring to Figure 3, a method for performing monitoring on tokenized bonds is disclosed.

In the case of tokenized ESG bonds, data on quantitative indicators can be generated that can be recorded in real time. For example, information on greenhouse gases, air pollutants, water pollutants, wastes, chemicals, etc., which are quantitative indicators that can be recorded in real time, is generated in real time, and the corresponding quantitative indicator API (application interface) is connected to provide the corresponding data. The validity can be verified and recorded on the blockchain.

In addition, through real-time reporting and comparison with other issuer's post-report data, the issuer's post-report evaluation data can be monitored by the bond monitoring node 150 and recorded on the blockchain. Additionally, effects based on post-report evaluation data for each bond tokenized through a smart contract can be automatically calculated.

In addition, tokenized bonds can be used as an authentication method. For example, tokenized ESG bonds held by a trader node can function as a means of authentication along with ownership information of the tokenized ESG bond. Accordingly, the scope of bond use can be expanded to membership participation during the issuer's promotions or events.

During trading, trading is carried out at a trading level that reflects the previous execution history of bonds of the same type and with similar periods.

Additionally, small bond transactions can also be supported by dividing tokenized bonds into decimal units so they can be traded.

According to an embodiment of the present invention, for bonds where issued funds such as ESG bonds are used for projects that create eco-friendly or social benefits, the status of fund use is confirmed through a blockchain system, and indicators showing the impact are shared, and further. Monitoring of investors may be possible using token incentives.

A bond monitoring device can record monitoring information about tokenized bonds on the blockchain. Monitoring information may include quantitative indicators for tokenized bonds, the issuer's use of funds, issuer post-report evaluation data, etc.

Figure 4 is a conceptual diagram showing a method of trading tokenized bonds on a blockchain according to an embodiment of the present invention.

In Figure 4, a method of performing bond trading on a bond trading node is disclosed.

Referring to FIG. 4, a method for real-time processing of bond transactions on a blockchain 470 is disclosed.

Bond transaction records are recorded on the blockchain 470, and a method is disclosed to process bond transactions in real time as much as possible.

Instead of the blockchain 470 for recording bond transactions, a non-blockchain database 430 and a blockchain 470 coexist to store bond transaction details.

The matching bond purchase transaction and bond sale transaction are also transmitted to the non-blockchain database 430, and transactions based on the non-blockchain database 430 can be performed primarily. Transactions before being recorded on the blockchain can be expressed in terms of primary bond transactions (450).

After the first bond transaction 450 based on the non-blockchain database 430 is performed, multiple matching bond purchase transactions and bond sale transactions can be recorded on the block in accordance with the block creation time, and on the block When recorded, the final bond transaction 460 is confirmed, and the tokenized bond can be transferred from the wallet of the trader node (sell) 410 to the wallet of the trader node (buy) 420.

A record of the final transaction and confirmed transaction is performed on the non-blockchain database 430, and the confirmed transaction record of the non-blockchain database 430 and the record on the blockchain can be synchronized and managed.

In this way, the completion of the transaction is delivered more quickly before it is recorded on the actual block, converting the actually traded bond to a provisional state, and the trader node (buy) 420 and the trader node (sell) 410 conduct the transaction. You can check completion more quickly.

In the present invention, cancellation of the transaction may be possible after the first bond transaction (450) and before the final bond transaction (470) is confirmed. In the case of the first bond transaction 450, the bond transaction information is before being recorded on the block, and there may be a transaction cancellation section after the first bond transaction 450 but before the creation of the block.

The block generation timing on the blockchain according to an embodiment of the present invention can be adaptively adjusted. The transaction cancelable section can be determined by considering the expected block creation time after the first bond transaction 450, and the transaction cancelable section can be adaptively changed depending on when the bond transaction occurred and when the block was created.

The section where a transaction can be canceled may be a section that can prevent transaction accidents caused by unintentional transactions such as Ogi. In the case of a transaction that is determined to be a transaction accident, the bond transaction node 400 may enable cancellation within the transaction cancellation possible period.

Figure 5 is a conceptual diagram showing a bond trading method according to an embodiment of the present invention.

In Figure 5, a method for predicting information about the transaction cancellation possible section for bond trading and providing it to the trader node is disclosed.

Referring to Figure 5, the bond trading node can predict the block creation time.

The blockchain for bond trading of the present invention can adaptively adjust the block creation time by taking into account the time when bond transactions occur and the time when bond transactions do not occur, such as bond trading hours and after-hours trading times. In addition, by additionally considering bond trading volume, the block creation time can be relatively adjusted within bond trading hours.

The bond trading node can determine the expected block creation time based on the block creation time that changes adaptively as above.

After the previous block creation time, the first bond transaction 510 is performed, records of the first bond transaction 510 are stored in the non-blockchain database 530, and bonds corresponding to the first bond transaction 510 are purchased. Transactions and bond sale transactions can be accumulated to be recorded on the blockchain.

The trader node (buyer) that generated the first bond transaction (510) allows cancellation of the transaction during the block creation time determined based on the expected block creation time (530) after the time of occurrence of the first bond transaction (510). The transaction cancellation option 550 may be activated in the transaction cancellation possible section 540.

The transaction cancellation possible section 540 is determined based on the expected block creation time 530, but the expected block creation time 530 is set to a certain section, and the transaction cancellation possible section 540 is the expected block creation time 530. It can be determined by subtracting the critical safety margin time from the fastest time among the sections set as .

The bond trading node may provide a transaction cancellation option (550) if it is determined to be an abnormal transaction. If the transaction is traded at a price above or below the critical range compared to the current price, it is judged to be an abnormal transaction and a transaction cancellation option 550 may be provided to the trader node (buy) and the trader node (sell).

Based on this transaction cancellation option 550, the trader node (buy) or the trader node (sell) can prevent trading accidents.

Figure 6 is a conceptual diagram showing a bond trading method according to an embodiment of the present invention.

In Figure 6, a method for adaptively adjusting block creation time is disclosed.

Referring to Figure 6, there may be multiple block generation consensus nodes to generate blocks on the blockchain.

In the present invention, records of transactions occurring on the blockchain are collected for each time zone, and block creation times can be adaptively determined for each time zone based on the transaction records.

Transactions can be classified into two types. The first type transaction 610 is a transaction in which block creation time is important and may include transactions related to transactions (a bond purchase transaction and a bond sale transaction). The second type transaction 620 is a transaction in which block creation time is not important and may include a transaction for recording information unrelated to a transaction, such as bond monitoring information, on a block.

The block creation time determination device 650 may determine the block creation time based on the transaction that occurs. The block creation time determination device 650 may filter the second type transaction 620, extract the first type transaction 610, and perform learning to determine the block creation time for block creation.

First, transaction time and non-transaction time are distinguished, and transaction time can be hierarchically divided to learn about the transaction volume that occurs by hour.

The block creation time determination device 650 may perform learning to determine the block creation time based on the first type transaction 610 and the block creation time when the first type transaction 610 occurs.

For learning to determine the block creation time, the first type transaction 610 may include transaction time information 620 and time layer information 630 regarding whether it is transaction time or non-transaction time. Time layer information is information that stratifies time units and can be used to stratify time units to perform block generation considering the time sensitivity of the block creation time.

The first time layer 633 is the smallest time unit and may be in seconds, the second time layer 636 may be in minutes, and the third time layer 639 may be in hours. Through the setup of these time layers, learning about block creation times based on sensitivity in seconds, learning about block creation times based on sensitivity in minutes, and learning about block creation times based on sensitivity in hours are performed. It can be.

The block creation time determination device 650 sets the time sensitivity (sensitivity in seconds, sensitivity in minutes, sensitivity in hours) and generates blocks so that the block creation time is less than or equal to the critical block creation time based on the learned results. . For example, when the block creation time determination device 650 sets the time sensitivity to a sensitivity in seconds, a block can be generated with the sensitivity in seconds so that the block creation time is less than or equal to the critical block creation time.

Figure 7 is a conceptual diagram showing a bond fragmentation trading method according to an embodiment of the present invention.

In Figure 7, a bond fragmentation trading method for fragmenting and trading tokenized bonds is disclosed.

Referring to FIG. 7, the bond fragmentation trading method discloses a method for dividing and trading one tokenized bond.

Fragmentation of tokenized bonds may be performed in order to split the tokenized bonds and trade them. The bond trading node may receive a bond fragmentation request 700 to fragment the tokenized bond from a trader node (sell) holding the tokenized bond.

The bond fragmentation request 700 may include a target bond subject to fragmentation and fragment information. The fragmentation information may include information generated during bond fragmentation, such as uniform fragmentation 710, non-uniform fragmentation 720, fragmentation ratio, and information on bond price after fragmentation.

Equal fragmentation (710) is to fragment bonds at the same price.

Unequal fragmentation (720) refers to fragmenting bonds at unequal prices.

The carving ratio is about the rate at which you carve the bond.

Bond price after carving refers to the price of the bond after carving.

When fragmentation is performed, a fragmentation request transaction is sent to the blockchain, and the bond can be fragmented based on a smart contract according to the fragmentation request transaction. Information on the target bond and fragmentation information may be matched to the fragmented bond, and fragmented bond identification information may be given. Fragmented bond identification information can be generated by considering the hash value generated by performing primary hashing based on the bond identification information.

In order to trade fragmented bonds, individual transactions can be performed on fragmented bonds, but transactions can also be performed by combining multiple fragmented bonds. When trading individual fragmented bonds, the transaction is performed based on the identification information of the fragmented bonds, and when trading multiple fragmented bonds by combining them, secondary hashing is performed based on the identification information of each of the multiple fragmented bonds. New fragmentation bond identification information can be given as a hash value.

Primary fragmented tokenized bonds can be expressed in terms of primary fragmented bonds. If the primary fragmentation bond is further fragmented, or fragmentation is performed once more, such as when the primary fragmentation bond is merged and then fragmented again, it can be expressed as a secondary fragmentation bond. In this way, the nth fragmented bond can be created through nth hashing, and the records of the previous tokenized bond from which the nth fragmented bond was created and the previous fragmented bond can be hashed and preserved.

There may be a price difference between trading fragmented bonds and trading one non-fragmented tokenized bond. For example, the price of n fragmented bonds combining to form one bond may be lower than the price of one non-fragmented tokenized bond. In this case, the bond exchange node may combine n fragmented bonds to create one tokenized bond and preferentially sell it to the trader node (buyer) at a low price.

Bond exchange nodes can create fragmented bonds that combine to achieve the lowest price and provide them to trader nodes (buyers). Alternatively, the bond exchange node can increase the trading activity of fragmented bonds by providing various combinations of the lowest price fragmented bonds where the combination of fragmented bonds subject to sale is the lowest price.

That is, in the present invention, considering the purchase amount of the trader node (buyer), the bond exchange node can combine fragmented bonds to be sold and preferentially sell them at a lower price than the actual bond.

When a transaction is performed by merging multiple fragmented bonds to be sold, the bond exchange node combines multiple bond sale transactions from multiple trader nodes (sellers) who are owners of multiple fragmented bonds and creates one bond sale transaction on the blockchain. You can complete the transaction by sending it to . Transaction activation of tokenized bonds can be performed through fragmentation in the same manner as above.

The embodiments according to the present invention described above can be implemented in the form of program instructions that can be executed through various computer components and recorded on a computer-readable recording medium. The computer-readable recording medium may include program instructions, data files, data structures, etc., singly or in combination. The program instructions recorded on the computer-readable recording medium may be specially designed and configured for the present invention or may be known and usable by those skilled in the computer software field. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical recording media such as CD-ROMs and DVDs, and magneto-optical media such as floptical disks. medium), and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, etc. Examples of program instructions include not only machine language code such as that created by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. A hardware device can be converted into one or more software modules to perform processing according to the invention and vice versa.

In the above, the present invention has been described in terms of specific details, such as specific components, and limited embodiments and drawings, but this is only provided to facilitate a more general understanding of the present invention, and the present invention is not limited to the above embodiments. Anyone with ordinary knowledge in the technical field to which the invention pertains can make various modifications and changes from this description.

Therefore, the spirit of the present invention should not be limited to the above-described embodiments, and the scope of the patent claims described below as well as all scopes equivalent to or equivalently changed from the scope of the claims are within the scope of the spirit of the present invention. It will be said to belong to

Claims (6)

How to trade bonds on blockchain:
The step where the bond issuance node transmits the bond issuance request transaction to the blockchain.
A bond listing node determining whether to list a bond based on the bond issuance request transaction and transmitting the tokenized bond to a bond trading node; and
A bond trading method on a blockchain comprising a bond trading node providing a trading service for the tokenized bond. According to paragraph 1,
The trading service is performed based on trader nodes (sell) and trader nodes (buy),
A bond trading method on a blockchain, characterized in that transactions for the tokenized bonds based on the transaction service are recorded on the blockchain. According to paragraph 2,
Further comprising the step of the bond monitoring device recording monitoring information about the tokenized bond on the blockchain,
The monitoring information is a bond trading method on a blockchain, characterized in that it includes quantitative indicators for the tokenized bond, the issuer's fund use history, and the issuer's post-report evaluation data. The blockchain bond trading system for bond trading on the blockchain is,
A bond issuance node implemented to transmit a bond issuance request transaction on the blockchain;
a bond listing node configured to determine whether to list a bond based on the bond issuance request transaction and transmit the tokenized bond to a bond trading node; and
A blockchain bond trading system comprising a bond trading node implemented to provide trading services for the tokenized bonds. According to clause 4,
The trading service is performed based on trader nodes (sell) and trader nodes (buy),
A blockchain bond trading system, characterized in that transactions for the tokenized bonds based on the transaction service are recorded on the blockchain. According to clause 5,
It further includes a bond monitoring device to record monitoring information about the tokenized bond on the blockchain,
The monitoring information is a blockchain bond trading system characterized in that it includes quantitative indicators for the tokenized bonds, the issuer's fund usage details, and the issuer's post-report evaluation data.

Images