We use lots of creative commons images from flickr. Here is a template email you might send to someone if you use one of their images.
Flickr image use email
You will need to login to Flickr and send this email through their contact forms.
[their screen name],
This is [your name] from the Science Museum of Minnesota. I'm just writing to let you know that we have used one of your Creative Commons photos from Flickr.com on our website, with a link to your page. You can check it out here:
[url]
Thanks for sharing your photos, and feel free to write back with any comments or questions.
[your name]
[your title if applicable]