Q:

How do I know if image from my site is getting cached by proxy servers?

The following is a http response header from a image on our company's website.
HTTP/1.1 200 OK
Content-Type: image/png
Last-Modified: Thu, 03 Dec 2009 15:51:57 GMT
Accept-Ranges: bytes
ETag: "1e61e38a3074ca1:0"
Date: Wed, 06 Jan 2010 22:06:23 GMT
Content-Length: 9140

Is there anyway to know if this image is publicly cacheable in some proxy server?  The RFC definition seems to be ambiguous http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9.1 and http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.4.

A:

Run RED on your URL and it'll tell you whether the response is cacheable, among other information.

