Instead of using an external program, I would like to take this chance to recommend the GD module. Here is a simple example that can be modified to easily do what you want and is a bit more Perlish than piping to fly.

#!perl
use warnings;
use strict;
use GD;

# create a new image
my $im = new GD::Image(100,100);

# allocate some colors
my $white = $im->colorAllocate(255,255,255);
my $black = $im->colorAllocate(0,0,0);   
my $red = $im->colorAllocate(255,0,0);  
my $blue = $im->colorAllocate(0,0,255);

# Put a black frame around the picture
$im->rectangle(0,0,99,99,$black);

# Draw a blue oval
$im->arc(50,50,95,75,0,360,$blue);

# And fill it with red
$im->fill(50,50,$red);

# draw a line (x1,y1,x2,y2,color)
$im->line(30,20,40,50,$black);

# open an output file
my $png_file = "/full/path/test.png";
open OUT, ">$png_file" or die "Cannot open $png_file:$!\n";

# make sure we are writing to a binary stream (Win only)
binmode OUT;

# Convert the image to PNG and print it on standard output
print OUT $im->png;
close OUT or die "Cannot close $png_file:$!\n";
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Disclaimer: I took this sample from the documentation somewhere and take no credit for it, although it is slightly modified.

-- Regards,
Helgi Briem
helgi AT decode DOT is