[link|http://httpd.apache.org/docs/1.3/mod/mod_alias.html#redirectmatch|apache 1.3 mod_alias docs]

RedirectMatch (.*)\\.gif$ [link|http://www.anotherserver.com$1.jpg|http://www.anotherserver.com$1.jpg]


Just add the parts you need.

But it appears you are good. Nothing a test wouldn't fix.