I hope everyone on all sides can recognise how absurd the "it's theft if you can recognise the original" argument is. For starters, photographers have a long tradition of claiming copyright in reference photos of fine art, where the whole point is to create an image which is as alike the original as possible.
Just replying to myself to clarify, here: the situation seems to be different in the US and in the UK. In the US, there is explicitly no copyright in a mechanical reproduction of an original artwork. It would appear that there is in the UK.
