I don't see a problem. If you put your work out in public without taking proper steps to safeguard your rights, it's public.
Take John Walker, for instance. He invented matches. Thinking that the public would be better off if he didn't patent his work, he allowed people to copy him. So, anyone could make a match.
If you take a picture and don't put your name on it, then put it out in public, there is not reason that other people shouldn't be able to use it.
It's the same way in the US. If I do a Google image search for an image of a sunset to put into my document, I can use pretty much whatever I find, as it is in the public domain. I only get in trouble if it's specifically marked.