V@no,
I think this is what ahmed_badawy is asking for because I have seen it when I have been surfing other boards but can not find one to save my neck to give you a screen shot of it.
In the comments section above all the comments there is a box that say "Thank you sent from" and then it has a list off all the members that sent the thank you to the person posting the pic.
I thought it was pretty cool but never looked into how they did it.
I would think on the comment form maybe make a quick button that says "send quick thank you" for registered users and then the list of thank yous would be listed on the details page above the comments...
Hopefully that helps explain it or if I am way far off I hope he will explain it better but either way I think it would make a good mod