Hi Mark Graham,
Thanks a lot, I appreciate your help.
I'd followed the instructions but I'm not sure where and how embed the code in the entry.php and entry_link_thumbs.php
note: I tryed to insert the code sketch that I wrote but the forum didn't let me. I used the raw but nothing, sorry.
And other question. This watermark is just for the thumbnails or is possible to use for the big image also?