Most of the time I just use Flickr. I search for what I'm looking for, then click the advanced search tab. Checking the "Only search within Creative Commons-lic

Most of the time I just use Flickr. I search for what I'm looking for, then click the advanced search tab. Checking the "Only search within Creative Commons-licensed content" limits the results to stuff that copyright owners are willing to let you use. Most of the time you just need a simple attribution with the image.