This article discusses finding the best free images etc. for your blog but I think it's appropriate for e-learning as well.
It also discusses Creative Commons Images - a set of free licenses that allow artists to share their work, while still retaining some of their rights.
Check out this article:
http://smackdown.blogsblogsblogs.com/2009/01/12/how-to-find-the-best-free-imagephotographics-downloads-for-your-blog-posts/
