There are many places to find pictures of constellations online, including EarthSky, Space.com and HowStuffWorks. It also helps to do a Google image search. It is important to consider that there are different types of pictures available, such as artwork, digital diagrams and real-life photography.
If a Google image search is used, it helps to be as specific as possible in order to retrieve the best and most appropriate pictures. Space.com and HowStuffWorks provide a variety of images, including artwork of the night sky from different historical time periods. EarthSky is a comprehensive site with a collection of illustrations specifically for the constellations of the zodiac.