Most of my personal images are licensed CC-BY. This means you can copy, distribute, and adapt them without requesting permission - though you do need to attribute them. You can attribute to either "Ryan Baumann" or "Flickr user ryanfb". Though you don't need to request my permission, I'm always glad to hear about how my work is being used, so feel free to drop me a line or a link.

I also have Creative Commons works from other people/projects hosted on this account, and in those cases I've made the best possible attempt to attribute according to their wishes, which you should do also instead of attributing me.

See this post for good general information on attributing Creative Commons works.