There are no 'public domain' photos. Everything is copyrighted. I go after people for copyright infringement almost on a daily basis, and probably 1/3 of the sites are chat forums like this. IF someone asked if they could use a photo with a link to one of my sites, I'd gladly say yes, but no one ever does, they just steal a photo from the members' area then repost it for everyone to look at - then it ends up on 20 TGPs within 24 hours and I end up having to file 20 DMCA notices.

Most webmasters I talk to say they don't mind if their photos are reposted with the URL on them.

Nothing pisses me off more than when someone removes my copyright notice/URL from a photo.