I have some thoughts on the idea of big corporations and us little guys.
They may send letters to big corps. but they have deep pockets and probably just pay it and make it and away for the most part, hence we don't hear about it much hear, they have legal teams that direct them...we don't.
I also believe they really depend on the "fear factor" by targeting small mom and pop businesses. naturally it freaks most people out, and most likely a large percentage roll over and pay, and a smaller % lands here, gets educated and fights..
It would not be good PR for a large corporation to get dragged into a suit for infringement, hance another reason to just settle and sweep it under the rug.
One case I am going to follow closely is the HAN v Moku-Aina case, they are a larger company that apparently run/manage resort hotels around the world, and they are fighting back on multiple fronts..so much for the fear factor here, you'll also notice that GI and the others rarely file suit over 1 or 2 images, again IMHO this is purely for financial reasons nothing more.
http://www.scribd.com/doc/76416831/Hawaiian-Art-Network-Vincent-Tylor-vs-Moku-aina-Properties-Complainthttp://www.extortionletterinfo.com/forum/getty-images-letter-forum/hawaiian-art-network-v-moku-aina-properties-observations/msg4989/#msg4989