mod_access_referer is an Apache module that understand the "Referer"
HTTP header, and grant or deny access based on the Web page that
refered the file.

The "Referer" HTTP header is sent by the browser to the server, and it
contains the URL of the resource from where the URL of the asked
resource was obtained. The document "Hypertext Transfer Protocol --
HTTP/1.1" RFC 2616 gives the following explanation:
     "The Referer[sic] request-header field allows the client to
     specify, for the server's benefit, the address (URI) of the
     resource from which the Request-URI was obtained (the "referrer",
     although the header field is misspelled.) The Referer
     request-header allows a server to generate lists of back-links to
     resources for interest, logging, optimized caching, etc. It also
     allows obsolete or mistyped links to be traced for maintenance. The
     Referer field MUST NOT be sent if the Request-URI was obtained from
     a source that does not have its own URI, such as input from the
     user keyboard."

WWW:	http://accessreferer.sourceforge.net/

 -- Alex Kapranoff <kapr@crosswinds.net>