I would imagine you're buying a copy of the photo in non-raw format, whether it be jpeg/png/whatever. If you don't have a RAW copy to post to the blockchain, it's impossible to steal it.

Hi tw04, yes thats right, though it will depend also on the terms of the sale / license given by the seller, which in some cases may give the full rights to the image including the RAW file in some cases. All of which is under the discretion of the seller. In the case that they did give rights to the RAW file, then that user is the only one who gets the RAW file data, its passed to them via an ethereum escrow contract

are you sure .PNG doesn't contain enough data to reconstruct a RAW file? I'm not...

Given that RAW can have 32 bits per channel and PNG only 16 bits per channel, it must be possible* to construct two different RAW files which render to the same PNG.

*Possible in the mathematical sense, it may not be practical.