One gets a sense of how complex copyright is by following the cases that come up in courts or in pretrial negotiations or in the news. Here is one, (a letter by Alex Curtis at Public Knowledge) responding to an editorial in the Wall Street Journal. I post the whole short piece because it makes the current law clear and emphasizes that the responsibility for identifying and claiming infringement is on the copyright holder.

Notice and Take Down' Lets Web Services Exist

our Dec. 1 editorial, "Google Search: 'Copyright'" missed crucial elements of the Digital Millennium Copyright Act (DMCA) and the concept of fair use when it comes to the posting of copyrighted material online.

The content industry fought very hard and largely won what it wanted in the DMCA. The trade-off for infringing content hosted by an unknowing service provider was essentially this: no liability for the service provider that expeditiously removes the infringing content after the copyright holder has been notified. This "notice and take down" provision allows most automated Web services like YouTube to exist. The take-down provisions effectively place the responsibility on copyright owners to actively identify infringement and notify the host services, all themselves. That's a fair trade considering they also have the weight of civil and criminal copyright law in their corner. It would be unworkable for YouTube or any other organization to have someone sit behind the curtain and approve every submission of copyright-able works.