This IS the problem.
Fotolia removed the watermark on thumbnails?
I don't remember any watermark on the thumbnails.
And
Shutterstock has not
Adobe stock has not
Dreamstime has not
iStock/Getty has not (and their "thumbnails are twice bigger that the one of the other sites)
Envato has not
CanStock Photo has not
Depositphotos has not
Bigstock has not
123RF has not
Zoonar has not
GL Stock Images has not
Alamy has not
Mostphotos has not
etc.
So, where is the problem?
Yes, fundamentally it is.
But personally I don't care a lot because I know that many of my images are used, or will be used, without my consent.
This is part of the game and, unfortunately, if I want to be part of the game I have to play it as it is
By the way my "So,
where is the problem?" was a little "ironic/sarcastic"