Just because an image is found on the internet, it doesn't mean that it is there for you to use without permission.
Although student work can often be considered Fair Use of a copyrighted work, it is good practice to always look for a statement of permissible use and/or a suggested credit line before using the image. (See the College Art Association's Code of Best Practices for Fair Use in the Visual Arts for guidelines to follow.
Can't find any? If possible, contact the copyright holder to ask permission (hey, it never hurts!), or failing that, find an alternative resource.
For more about copyright:
To cite your image in-text: