Are they free? Yup, they're free. The photographer doesn't protect his or her rights to the images. They are free to use as you please. Are they poor quality? Not necessarily. Some of the best images on the web are in the public domain. Are they old? In fact, some of the most powerful photos today are taken from public domain pictures of yesteryear—What's the catch? Well, if you're using a photo that is definitely copyrighted in your content, you could possibly be sued for copyright infringement. Which is why it's really important to have a good understanding of what you can and can't do with them (click on!).