One thing you need to be careful of is redistribution. If you plan on using the images on a product – i.e., one that you will sell (whether on or as part of a physical printed product, or as part of a web to print service, such as www.skinit.com, or as part of artwork that will be sold in publication, say, for example, using royalty free illustration as part of a masthead that will appear on a printed newspaper or magazine).

Also, iStock will show you the # of downloads and popularity of RF images they sell. So, if you don’t want to select an image that you’ll likely see on other websites, in ads and in various marketing materials from other entities, steer clear of the most popular downloads.

I’ll preface this message by saying that I don’t have much experience using stock photos, but when I did need some I found ‘em at  http://www.sxc.hu