A Mickey mouse shot is a term used in the adult content industry, and is a legal requirement for producing, filming and broadcasting adult content for most media (online, broadcast and DVD distribution) in many countries. In essence, it is a way of proving the age of a model at the time of the shoot.
Mickey mouse shots are done by taking a newspaper of the day of the shoot, and panning the camera across it, proving the earliest date the footage could have been recorded. In the same shot (i.e. without cutting or editing), the camera pans to a head-and-shoulders view of the model, who is holding up two forms of identification next to their head. The camera then zooms in on the left ID, then zooms out to get a close-up of the model's face, then zooms back in on the right-hand ID.
The name 'mickey mouse shot' comes from the vague resemblance between the Disney character's ears and a model holding up the two forms of ID next to their head. Why two forms? Well, it's difficult to do a good forgery of one type of identification, but nearly impossible to convincingly forge two!
The Mickey Mouse shot footage is kept on file, and has to be supplied on DVD or as digital files to any content provider or distributor, especially in the US. In practice, a well-shot and clear mickey mouse shot places the responsibility of the model's age squarely on the model's shoulders, as the content generator, provider and distributor can point to due diligence.
If a content provider gets in legal trouble for distributing material of minors, despite of having a 'mickey mouse' shot of an adult performer, they can seek legal recourse from the model or actor.