DMCA is an acronym for the Digital Millennium Copyright Act. It was instigated and passed in America in 1998, although started it’s life in 1996, under the Clinton administration. The act was set up to modify the existing copyright act in light of the methodology behind the working actions of the internet. There were a great deal of large companies that were being sued over copyright infringements, even though the content was UGC (User Generated Content). What the DMCA did was take the onus off the large companies and placed it into the hands of the User to validate and be responsible for the content that was placed online.
This is quite complicated to describe, but most is stated in the Terms of Service that many sites place on their footer areas, as a guide to UGC being put on the site. The good points about the DMCA are that many countries abide by it, even though it is a US based law. Countries that have signed the Berne Agreement tend to uphold any inquiries related to DMCA requests. Also, many countries and companies that fall under the countries of participated bodies of the DMCA, have to by fact of the DMCA set up DMCA based registration service. This means that any DMCA take down request that enters a company, that is situated inside the DMCA acceptance zone has to file the DMCA legally, and act upon the content.