Section 512 Overview
Section 512 contains a number of safe harbors that eliminate liability if Online Service Providers comply with certain conditions. These are completely voluntary, but of course one may be subject to copyright infringement lawsuits if one doesn't comply, although defenses can still be raised. An Online Service Provider can be any website, email provider, or anything else that operates online, as distinguished from an Internet Service Provider, which are companies such as Comcast and Verizon that connect customers to the internet.
§ 512(a) -- Transitory Network Communications: The OSP is not liable for automatically-made, unmodified copies created due to another's action. Example: Alice uses Gmail to send a copyrighted work to Bob. In the course of sending the message, Gmail copies the work in its internal email-routing processes. Gmail is exempted from liability by § 512(a).
§ 512(b) -- System Caching: The OSP is not liable for caching copies if they are made available by another and transmitted at the recipient's direction, provided that the OSP complies with the owner's conditions and disables access on notice of a court order. Example: Alice subscribes to Comcast, and downloads a copyrighted work. Comcast automatically caches the work in accordance with its standard caching algorithm. Comcast is exempted from liability by § 512(b).
§ 512(c) -- User-Uploaded Content: The OSP is not liable for infringing material that is hosted on its servers if it is uploaded by users, if the OSP takes down material that it knows or should know is infringing, and if the OSP complies with notice-and-takedown procedures. The notice-and-takedown procedure has been criticized as stifling free speech because takedown notices can be issued even if the work is not infringing, for example if it is fair use. Example: Alice uploads an episode of her favorite show to YouTube. YouTube receives a DMCA takedown notice from the copyright owner, and quickly removes the video. YouTube is exempted from liability by § 512(c).
§ 512(d) -- Links and Indices to Infringing Content: The OSP is not liable for linking to or indexing infringing infringing content, provided that it follows the same takedown procedures as for section (c). Example: Alice searches Google and comes across a song she wrote being hosted by an infringing website. She submits a DMCA takedown notice to Google, which promptly removes the link. Google is exempted from liability by § 512(d).