This isn't exactly a perl question, is it?

Well, I guess it could be if you use mod_perl and set up some handler to replace some variable in your .html or .shtml with the document's http_referer. But nevermind ...

What you are clearly looking for is the SSI howto (http://httpd.apache.org/docs/howto/ssi.html) and the mod_include docs (http://httpd.apache.org/docs/mod/mod_include.html). The include variable will be something like ${HTTP_REFERER}

Oh, and I'm assuming that you're using Apache or perhaps some close relative thereof.

Not that I disagree with ichimunki in any way. Remember, some people turn off images and won't ever be counted by your script.