Get permission [July 24, 2012, 5:51 a.m.]
So you've stumbled on a few photos that you can use -- or maybe you were lucky and found the perfect one for you needs. Do you have the rights to reuse the photo? What are they? What can you do with the photo? What can't you do with the photo? Do you have all the rights you need for your specific use of it?
Remember, with CC licenses you are already granted certain permissions in advance, which means you don't have to ask for permission as long as you follow the conditions of the license. You might realize you need permission beyond what the license has granted; in those cases, you will either have to ask the author for permission or find a different photo that does give you the permissions you need.
Something to keep in mind: Don't assume that anything you find on the web is correctly marked, eg. that a photo is by the author and under the terms stated. You should always verify that the work is actually under a CC license by following the link(s). Since there is no registration to use a CC license, CC has no way to determine what has and hasn't been placed under the terms of a CC license. If you are ever in doubt you should contact the copyright holder directly, or try to contact the site where you found the content.