Now that was nice, however what does copyright mean for images?
In short: Everything. Because any image that you may see on the web may possibly be copyrighted. Unlike movies or music, there is no fair use for images, no matter how much you change or alter the image it still belongs to the copyright holder. (see US Copyright Law) So if you were to talk about 15 sec of video, like this movie does it is well within fair use. If you were to make a parody of a popular song, the same applies. Images are a little stickier, because the image's creator has the sole right to make derivatives of the work.
However there is a way to have images available for your blogs and papers, free from the irritation of copyright... there is something called "creative commons" where people are willing to put up their images with minimal limitations on their reproduction for people to use them. You can read more about the Creative Commons movement HERE and find creative commons images in many different locations such as Flickr, Corbis, and more if you look at google.