Perl CGI script to respond to erroneous Base64 image requests
The only real problem I see is that if the browser is really "last century" it probably won't support a long enough query string to contain the full image. So your returned image might be incomplete. Another thing is that this would waste a lot of bandwidth.

I see two options


To suppress those error messages you could just handle those URLs like you and make a header redirect (to use the browser cache!) to an error/empty image.
Use conditional comments to load inline images on IE &lt; 8 with a normal img:src attribute. Since your culprit is most likely an Internet Explorer (people who install alternate browsers usually keep them up to date)


I would use the first actually, as it does not involve changing code.

To test whether your solution works, start Internet Explorer (9), open the Web Development tools, and dial it back to IE 6 or 7 (best try both)