In How to Spot Fake Screenshots students learn why people or organizations post fake screenshots. The lesson also teaches students four clues to look for to determine the validity of a screenshot. Finally, students learn how to use tools like FotoForensics and the Wayback Machine to determine whether a screenshot is real or fake.
Speaking of the Wayback Machine, it's one of the tools that I used to expose a DMCA email scam last spring. You can read more about that scam and how I unraveled it here.
Video - A Short Overview of the Internet Archive Wayback Machine