The popular clip art collections (such as Clipart&more 3.5 Million) sold on Amazon prohibit use of their images in computer software. I am developing an educational software that will use lots of images. Is there a cost-effective way to acquire the images that I need? Thanks in advance for your answers.
It depends what sort of images you need. Places like alamy.com have royalty-free images, but you may pay a few hundred dollars for the rights to each image.
Places like http://www.fromoldbooks.org/ have a lot of pubilc domain images (and some are copyrighted, watch out!), and there are lots of lists of sources of free clip art floating around.