Image authentication importance increases as image acquisition becomes easier with the help of new technologies. Today, almost any phone has a camera with decent performances and sharing images is encouraged by social media. Image tampering is also decreasing in difficulty because of the advances in image editing software. Today's signature-based image authentication techniques rely on storing the image signature until the authentication is needed. This is a disadvantage because the storage support is usually unique, controlled by one entity and could fail. Also, this centralized approach is not fundamentally trustworthy. To solve these problems, the paper proposes a signature-based image authentication method resistant to JPEG compression which makes use of new blockchain technology to store the image signature. With this method, the signature is stored in a decentralized network, significantly increasing the security.