Firstly he is not putting his personal name all over the photo's so is in no way claiming that he alone took the photo's, secondly you will find that the watermark also serves the purpose of deterring others using the photo's without permission of the website (we all know how to right click and save an image don't we??) so they can credit it as there own. Thirdly at this point in time the copyright laws that govern images, music, movies and the like that are loaded onto the web are still very undefined, so if you sent this image to a friend who then sent it to another friend and so forth and so forth what is stopping anyone who has a copy of this image sending it to Amnesia claiming it to be there own work..The answer Nothing at this point in time.
You say you are an artist yet you claim the picture is not a good one (something that baffles me) yet if you were an artist then you would know most of this it's the same with photo's on FB....

"Your born, You Live, You Die, given this premise, one can conclude since we have no control over when we are born and when we die, the only thing that matters to us should be how we live, simple really?" Mis-Cat to her philosophy Lecturer.