Sidney Crosby (Creative Commons Retouch from Vanluven), originally uploaded by DarthLen.
Online photo sharing site Flickr (as if there's anyone who doesn't know what it is) allows you to apply a Creative Commons license to any pictures you've uploaded. Obviously I'm more than happy about this as I've been a Creative Commons fan for some time based on my belief that traditional copyright laws are fundamentally flawed, but it does raise an interesting issue.
Flickr lets you choose a default license for any work which you upload, and also lets you change the copyright license for any given image at a later stage. So you upload some pictures from your holiday in Micronesia that get a traditional copyright applied to them by default, which you can then - if you wish - change to a less restrictive CC license at a later stage. This seems awfully convenient - and it is - but the point I'm trying to get at lies in the ability Flickr users have to change which license gets applied by default.
If you're a progressive-minded person and you decide that the majority of pictures you'll upload to your Flickr account will be under, say, a Creative Commons Attribution license, you'll decide it's far more convenient to change your default license to that and save yourself some effort in the long run. Big fucking deal, right? Well, actually yes. See, Creative Commons allows you to relicense your work at any time you want as long as you license it under a less restrictive license. So if you have a picture of your pug Larry under a CC Attribution NonCommercial Share Alike license, you are free to change that later on to an Attribution Share Alike license, which is less restrictive, but not an Attribution No Derivative Works license which is more restrictive and thus incompatible with your original license; at least not without a convoluted mess of legal headaches. In Creative Commons' own words:
"Creative Commons licenses are non-revocable. This means that you cannot stop someone, who has obtained your work under a Creative Commons license, from using the work according to that license."
Obviously this is to prevent you from fucking over (either accidentally or otherwise) parties who have already made use of your CC licensed work under the originally specified terms, by taking away rights you've already agreed to give them.
I have no doubt that Flickr added this option to make the lives of its users a bit easier, but in the process gave all of us the legal equivalent of a broken-glass encrusted enema with a bullet-shaped tip for easy insertion.
So what do I recommend? What I do is to leave my default license to standard copyright. Sure this leads to a bit of extra work whenever you upload images you wish to have under a Creative Commons license (it's hard work having to perform two extra clicks, you know), but at least you won't be violating CC relicensing terms, screwing anyone who wants to use your work, nor getting screwed by them.