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

sub sizePNG {
  return unless $_[0];
    my ($width, $height);
    ($width, $height) = unpack( "NN", $1 ) if $_[0] =~ /IHDR(........)/;
  return ($width,$height);
}

sub sizeGIF {
  return unless $_[0];
    my ($width, $height);
    ($width, $height) = unpack( "SS", $1 ) if $_[0] =~ /^GIF8..(....)/;
  return ($width,$height);
}

sub sizeJPG {
  return unless $_[0];
    my ($width, $height);
    ($height,$width) = unpack( "nn", $1 ) if $_[0] =~ /\xFF\xC0...(....)/;
  return ($width,$height);
}

sub get_file {
    open FILE, $_[0] or die $!;
    binmode FILE;
    local $/;
    my $data = <FILE>;
    close FILE;
  return $data;
}

my $gif = 'c:/sample.gif';
my $data = get_file($gif);
my @res = sizeGIF($data);
print "$gif width $res[0] height $res[1]\n";

my $jpg = 'c:/sample.jpg';
$data = get_file($jpg);
@res = sizeJPG($data);
print "$jpg width $res[0] height $res[1]\n";

my $png = 'c:/sample.png';
$data = get_file($png);
@res = sizePNG($data);
print "$png width $res[0] height $res[1]\n";