When I started out with Wikipedia, I knew nothing about copyright. "Fair use" to me meant "I want to use it, and it's not free." Like Many users however, over my time editing Wikipedia, I've gotten a crash course in copyright law. I've really gotten to appreciate the merits of Free Images over Fair Use ones, I think I finally "get it."
In my experience, the most helpful things in the world have been the UD government's decision to make all of their work the public domain, and Flickr's ability to search only creative commons, cc-by and cc-by-sa images. Try it yourself: USA.gov (make sure you're using federal government photos), and Flickr (check all three boxes in the Creative Commons section). These two resources provide mountains of free content.
Also like many other Wikipedians, I've encountered images that I would love to use, but were copyrighted. When no free content is available, a flickr search usually reveals some good content, if unfree at the time. Through following processes detailed at Wikipedia:Requesting copyright permission, I've been able to get every image I've asked for so far acceptably licensed (usually under cc-by-sa). Below are images originally unfree, but a simple "please" released them. There may not be a lot of them (they'll increase as times goes on), but there are a lot of users like me, and we've accumulated thousands of now-free images, just because we asked.
