#!/usr/bin/perl -w
use Imager;
use strict;

my $file       = "something.jpg";
my $thumb_file = "something_thumb.jpg";

my $image = Imager->new()
   or die "Can't create Imager object";
$image->open(file => $file) or die $image->errstr;

# You could also pass qtype => 'preview' to scale() to
# supposedly make a smaller thumbnail (filesize wise)
my $thumbnail = $image->scale(ypixels => 100)
   or die $image->errstr;

# You could pass fd => fileno(STDOUT), instead of the file
# parameter if you need to print to STDOUT.  If you do so
# make sure to binmode STDOUT, and disable buffering ($|++)
$thumbnail->write(file => $thumb_file, type => 'jpeg')
   or die $thumbnail->errstr;