Meh, if the guy wants to post "borrowed" pictures that he applied filters to and call it art - good for him. I play around with borrowed (or screen capped) images on my blogs - granted, I generally add captions, use them to enhance articles I write, and don't claim they're art, original, or mine; so they likely fall under fair use. (I also do a *bit* more work than apply a filter... ) But, hey, what he's doing is a victim-less crime.
Why the outrage? So he's a talentless hack pretending to be an artist. The guy clearly has issues - either serious ones, or just insecurity. We've all been there. We've all scribbled down bad poetry and made "masterpieces" out of old filtered photography. If it helps him to post it on a forum, good for him. He's not going to get famous for stealing a picture he found on google - he doesn't stand to make any money off of it - the pictures he's messing with are freely available and the warped bastard children of those pictures are being made freely available. It's not like he's selling t-shirts and prints. He's not selling them to magazines or ad companies. No one's going "No! he stole my photograph and claimed it as his own. Now I can't make a living!"