Richard, this sounds like a cool idea for a site for yourself. Just be sure to do the good folks who give you permission to use their pics the courtesy of saving the pictures and uploading them to the server where your site is located. One extremely common problem on the web is what's known as "direct linking" to images. This is when someone sets the image source in their HTML document to call for the image from somebody else's server. Obviously enough, the majority of the people who do this just don't know any better. But the effect this has is to steal bandwidth from the person you're "borrowing" the picture from. As a web designer, I can tell you how critical bandwidth can be, especially for a site that already gets a lot of traffic. I'm sure Mike and Spark can attest to how expensive bandwidth can get, especially when your bandwidth is being used to serve images that aren't even on your site.
You can win a lot of points just by doing this small courtesy (which is in reality, a big help).
Good luck with your site!
Regards -- Shades