This paper proposes a blockchain-based traceability system of photos. Thanks to a novel scheme that securely chains certificates of image data originating from a trusted origin certificate, the system authenticates the provenance of original and converted images, e.g., which digital camera created it. The system requires a Public Key Infrastructure (PKI) of digital cameras to authenticate the trusted origin certificate signed by the certified digital camera. It does not require a PKI of image conversion software. The proposed solution is suitable for the traceability system of photos on the Internet as the scheme of chaining certificates applies to any image conversion software, including open source-based photo editing applications and cloud server software that converts image data of photos. We have implemented a prototype of the traceability system using Ethereum as a permissioned blockchain and evaluated the system's feasibility.
