Holy crap, I thought the textarea in the message 
body had hard breaks, unless Yann changed it or 
something. (?)  -_-; I'll try again: 

This has been brought up before, and I suggest 
anyone remotely interested in techniques for 
watermarking/stamping use the SEARCH feature at 
the bottom of the forum page to look for these 
threads (you can search by 'watermark', 
'branding', 'stamping' or by author - oion, since 
I was involved in at least a few of them). 
Unfortunately I removed the demo images.. It's not
foolproof (depending on how you do it), but can 
save a bit of headache/heartache later.