I understand putting something on a photo if you want to identify it as yours but unless you make your living off your photography or have photos of something spectacular and rare, I don't see why people worry so much about someone else posting a photo and claiming its theirs. Sure it's lame and if I found someone posting pictures of my dogs and saying the photos were theirs I'd say something to them, but it's not something I'm going to sweat over trying to prevent. I personally think smacking a water mark in the middle of a picture just to post on a forum is a bit much, and it truly does distract away from the photo for me. I can certainly understand when a pro photographer with an online gallery to showcase their work does it though.