1st Perl script:

use strict;
use warnings;
use CGI qw/:standard *table *Tr *td/;
use CGI::Carp qw(fatalsToBrowser);
use Date::Manip; 
use DBI;
use GD::Graph;
use GD::Graph::bars;
use GD::Graph::lines;
use GD::Graph::histogram;
...
(snip HTML and form generation code plus database interrogation code)
...
    my $graph=GD::Graph::bars->new();
    my $format=$graph->export_format;
            $graph->set    (
                              x_label=>'Uploaders',
y_label=>'Total number of uploads'
                    );        
            @bar_data=(\@x-axis, \@bars);

my $gd=$graph->plot(\@bar_data)->$format() or die $graph->error;
print '<img src=http://foobar.com/foobar.pl?image=$gd&format=$format>'
+;#sends the parameters to the second script
[download]

#!/usr/bin/perl -w

use strict;
use warnings;
use CGI qw(:standard);

my $image=param('image');
my $format=param('format');

print header("image/$format");
binmode STDOUT;
print $image;
[download]

Any ideas as to what I'm doing wrong?

my $gd=$graph->plot(\@bar_data)->$format() or die $graph->error;
print '<img src=http://foobar.com/foobar.pl?image=$gd&format=$format>'
+;
[download]

$gd is a GD object, not the image itself. And you can't pass the object around as an URL parameter.

Likewise you can't pass the image itself around as an URL paramter, because it's massive binary data. Instead you have to create the image in the second script. Or you store it on disk in the first script, and just print the URL of the created image into the HTML.

Thanks, moritz. I'd tried the first method, with only temporary success. I'll therefore try the second method, since it looks like a very neat way of solving the problem. (BTW I thought $gd was a pointer to the image and that you could therefore pass it as a parameter. Obviously not.)