But you are signing it with your _private_ key, presumably. You know, the key that stays on your device and nobody knows?
If you sign two images with that private key, people will know for certain that you created both of them. This is the whole point of signing something. No one else can fake it because they don't have the private key, but EVERYONE can verify it because they DO have the public key. In fact, they don't even need the public key because they can extract it from the signature and the signed image.