If you want to return a 1x1 blank GIF image instead of a bitmap, you can try the following:

  use MIME::Base64 qw(decode_base64);
  print "Content-type: image/gif\n\n";
  print decode_base64
    'R0lGODlhAQABAID/AMDAwAAAACH5BAEAAAAALAAAAAABAAEAQAICRAEAOwA7';
[download]

I'll admit it is not quite as pretty as the bitmap version though!

- Cees