How to force a web browser NOT to cache images

Question

Background

I am writing and using a very simple CGI-based (Perl) content management tool for two pro-bono websites. It provides the website administrator with HTML

Answer 1

Your problem is that despite the Expires: header, your browser is re-using its in-memory copy of the image from before it was updated, rather than even checking its cache.

I had a very similar situation uploading product images in the admin backend for a store-like site, and in my case I decided the best option was to use javascript to force an image refresh, without using any of the URL-modifying techniques other people have already mentioned here. Instead, I put the image URL into a hidden IFRAME, called location.reload(true) on the IFRAME's window, and then replaced my image on the page. This forces a refresh of the image, not just on the page I'm on, but also on any later pages I visit - without either client or server having to remember any URL querystring or fragment identifier parameters.

I posted some code to do this in my answer here.