-Photos for sale are identified as rightfully owned by having RAW file details published to the blockchain (actual High Res image is not stored on chain)
Look at Steemit for examples of people making money from original content.
I don't see the way how this could be implemented to blockchain. If every blockchain node downloaded and compared all images It would create massive bandwith and need for cpu/gpu power. Or am I missing something?
The remedy, in other words, remains legal. I see this as a tool for facilitating legal remedy. (Or have I missed your point completely?)
That's not enough. What if someone publishes before the author. Say I buy something from other resource or even directly and publish it on the OP's.
Then the only benefit is the creator has got proof of the creation date, the pirate couldn't prove they created the content before that date.
I note they also only display low res until you buy a high quality version. That's what I do too. If someone wants to save/share my low res images its no problem. If they want something magazine or billboard res (ie commercial) they have to come to me.