I am writing a slide-show like application for android phone which I am going to sell. it will target very narrow audience and I do not think I will sell more than 1000 copies of it. I was going to buy pictures for it from microstock agencies like istockphoto but it turned out that they require purchase of “extended license” if you want to put their images into apps. And guess what? extended license runs from $70-100 per image!
so my question for you, where did you get images for your apps you want to sell?
You can search at creativecommons.org for images you can use “for commercial purposes”.