Referer source in HTTP protocol

The Referer header contains the URL of the request source. If you navigate from one page to another, Referer will contain the address of the first page.

Often, websites install software that analyzes Referer and extracts various information from it. For example, the website owner gets the opportunity to find out what search queries, how often, and what pages people get to.

If an HTTP client downloads an image from a server, presented on some page, then Referer will contain the address of this page. Some servers analyze Referer before issuing the image and do not show the image if the request comes from another site (and, for example, show a small placeholder image).