well, the site is more or less a Polish equivalent of 9gag. The picture has been uploaded by a user named 'Jakubcio'. To write a note to the said user directly you'd have to create an account there I guess. But you can always contact the admins by clicking here [link] , maybe they can do something?
well, adding huge watermarks will be to the detriment of your detailed art, but on the other hand I perfectly understand the feeling when your art flows freely as an anonymous pic over the internet. I try to use the dA watermarks whenever possible, but it does not solve the problem satisfactorily I guess