All my photographs are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
This means you're welcome to use my images for non-commercial purposes as long as you list me, John Arnold, as the creator. You're also allowed to make derivative works (crops, re-processing, composits) as long as the resulting work is also released under this same license. Non-commercial use means any use where you don't make money. If you're in doubt whether your use counts as commercial then drop me a line at email@example.com and I'll be happy to discuss the issue.
Most of my images are also available for licensed use with a fee if you do want to use them commercially. Please get in touch if there's an image you're interested in using commercially by emailing me at firstname.lastname@example.org.