Along the lines of my other question, I was wondering what the legal guidelines are on embedding images in StackExchange questions and answers. Many questions and answers here are greatly enhanced by including an image of what we're talking about. However, most of the photos you find in a quick Google Image search are copyrighted and have restricted use outside of their original context. Wikipedia seems to say that hotlinking images doesn't cause any legal problems in terms of copyright.
How are images embedded on StackExchange posts, and are there any legal considerations with searching for images and including them in questions and answers?