That's annoying - the server certainly knows that it's image/png:

$ lynx -head -dump "http://empeg.comms.net/files/80014-jemplode.png"
HTTP/1.0 200 OK
Date: Tue, 19 Mar 2002 19:06:59 GMT
Server: Apache
Last-Modified: Tue, 19 Mar 2002 18:39:06 GMT
ETag: "18a33-145e-3c9785ca"
Accept-Ranges: bytes
Content-Length: 5214
Content-Type: image/png

But it's not happy to get it right when uploading...