Stock Photo Talk has an interesting post out from Bahar Gidwani of Index Stock Imagery regarding the increasing options in the stock photography world away from Getty Images and Corbis. Apparently one of the disadvantages to buying images from Getty (considered the world wide leader) is that you must maintain an ongoing subscription with them in order to keep your images in compliance. If you buy a Getty Image and then use it and then your subscription lapses then it would appear that your rights to use a previously purchased image would come into question if it were still in use.
I’m just beginning to learn more about the stock photography business but this would not at first glance seem to be the best model by which to purchase photographs to use.
The issue you bring up concerns only the subscription stock photo service of Getty. Individual images can be purchased for a one-time fee for use on an unlimited royalty free basis