Most of my photos here are licensed "CC BY-SA ", Creative Commons, Attribution-ShareAlike (more info here). Feel free to use them if you want. Please credit me and mention or link to the CC BY-SA license. An easy way would be to make the photo itself a link back its Flickr page, where all this info can be had. If you want you could say something like "photo by Pfly", with a link to the photo's Flickr page. Thanks!