Many of the newer SE2.0 sites are well-suited to questions and answers containing images, and I love that many users use images in their posts. It can add value both for context and aesthetics. Examples:
- View the Grand Canyon by helicopter - is it real?
- Is it safe to travel in Greece during the riots about government spending cuts?
- How could I explore the Rock Islands of Palau?
- How can I control thistle in a lawn?
(ok, the last two are mine)
But, I think the licensing issue is a bit worrying. Obviously Stack Exchange is very aware of licensing and all content posted by users is licensed under CC BY-SA 3.0. However, there is little control over ensuring that users hold the right to license the images they post, and many images are of dubious source.
Wikipedia has extensive image use policy to ensure that the images that make it onto the site are allowed to be there. Images must be accompanied with sourcing info when uploaded.
As far as I know, Wikipedia images are free to be used here, and there are many great images available on Wikipedia, but we can't know that that's where they are from unless the user says so. And, the license most likely requires linking to the source/author.
- Should Stack Exchange require that images not owned by the user be accompanied with source and/or licensing info, and what do we do about existing unsourced images?
- What is the proper way to indicate the source or license of the image?
- (Added after Adam's answer) If requiring licensing info seems too onerous, should SE at least suggest or recommend sourcing so that images that are completely valid (i.e. Wikimedia Commons) have the proper attribution and the posts that use them can be worry-free should future issues arise?*
* I would recommend this approach at the very least, since if SE ran into image licensing troubles in the future, finding the source after-the-fact would be near impossible and unreferenced images would simply have to be removed.