recommendation for validator

When I put <img src="http://www.w3.org/Icons/valid-html401"> in my HTML documents, is there any reason this URL cannot refer to a script or program that checks HTTP_REFERER for validity and returns true and false graphics accordingly? This real-time validation would be valuable for large websites where it may not be practical to check manually on every page. 

Sincerely yours,
Aaron Grahn
http://www.aarongrahn.com/