License: Attribution, Share Alike
I am happy to share my photos with Wikipedia on the same terms that I share them here on Flickr.
That is, people can use, re-use, or mash-up my photo but they can't steal it. If they use a photo, they have to acknowledge that they got it from me.
There is a reason for making this claim, because without it you can lose control of your own work, even see it get copyrighted by someone else. Lubos Motl took a wonderful picture of Sidney Coleman, which he generously uploaded to Wikipedia. It has been republished without any credit to Lubos in many places. So somebody who had seen that photo on Harvard's website then wondered if Lubos had "stolen" the photo from there. Nope, it was the other way around.