I was sent an invitation through Flickr to start selling images with Getty. I have had a few images for sale on Alamy for a while but not much has come of that. I haven't really been very active on there either. They weren't accepting many of my images so it was a little frustrating. Since Getty has a partnership with Flickr it makes submitting images much easier.
I saw this blog post on the Flickr blog back in November stating Getty had a pool where you can submit photos to be considered as a contributer. Almost 2 months later I got the invite and they had selected 15 of my photos in my Flickr stream that they thought would make good stock photos. I don't know that I would agree with their selection on some of them though. They ended up not choosing any of the photos that I had submitted to the initial pool but the pics must have caught their eye since they went through my stream and chose others. Some of the photos they chose were from 2007 and really not as good as what I have posted in the last two years.
I have to fill out model and property releases for any photos that have recognizable people or buildings in them, even for self portraits. They are a bit of a pain to fill out and it will be a chore to get releases signed. I currently have 12 photos up for sale which is already more than I have on Alamy. I'm hoping the sales will be better too. I may pull my images off of Alamy and send some of those to Getty instead.