The Source Of The Video

The footage that appears on You Tube tend to be from one of the following sources.
1. The users own recorded material from scratch.
2. Material taken from another source e.g a user uploading clips of The Simpsons.

When footage is taken from another source it is most of the time copy written, and used without the owners consent, thus it being illegal to distribute, for whatever purpose. This is a constant problem of digital data (depending on your opinion). Because with digital data you can distribute multiple copies to others, which means people are not paying any money to the rightful owner. This is known as a form of piracy.
Piracy is an extremely hard activity to police within You Tube if there are so many users constantly uploading content. There is a system in place in You Tube for users to flag up a video if they think it's pirated material, but I believe users want grass on each other, after all the material is for them to watch.

It didn't take long for major entertainment companies to discover what's happening and start phoning their lawyers. Some companies tried to sue You Tube, however as far as my research goes no one has actually successfully sued You Tube. Although many companies have asked You Tube to remove videos that are online without their permission.

Viacom and the British Broadcasting Corporation both demanded You Tube to take down more than 200,000 videos. Taken from http://en.wikipedia.org/wiki/You_Tube#Copyright_infringement