CGI generated image/png problem?

[R.P. Aditya]

I have a simple script dynamically generating a PNG based on form input:

--------------------
  #!/usr/bin/perl
  # genImage.perl
  use strict;
  
  print <<LLI;
  Content-type: image/png
  
  LLI
  
  genPNG(); #a subroutine that can produce PNGs using libpng
--------------------

this worked fine before I used mod_perl. I've tried using:

  $q->header('image/png');

instead of the print "Content-Type" line, to no avail.  Annoyingly enough, if
I generate a jpeg ($q->header('image/jpeg')), albeit with a different library
routine, it works fine...

Other possibly relevant details:

Apache/1.3.12 (Unix) mod_perl/1.23

and in httpd.conf:

<Files *.perl>
   SetHandler perl-script
   PerlHandler Apache::Registry
   PerlSendHeader On
   Options +ExecCGI
</Files>

I've even tried with PerlSendHeader Off and adding "HTTP 1/1 200 OK" headers
with the same result -- jpegs work fine, PNG does not...

Clues? I suspect it's a problem with the PNG production and some intereaction
between mod_perl and the headers that stock Apache doesn't encounter, but will
be most interested if there might be another explanation or solution.

Thanks,
Adi