glitch.pl

use strict;
use warnings;
use Compress::Raw::Zlib;

my $file_name = shift;
my $opt_name = "glitched_".$file_name;

open (FH, $file_name) or die "$!";
binmode FH;
my $hoge = *FH;
my $len = (-s $file_name);
my $buf;
read($hoge, $buf, $len);
close FH;

sub jpeglitch{
  my $jpg = shift;
  $jpg =~ s/1/2/g;
  return $jpg
}

sub pnglitch{
  my $png = shift;
  my @data = split(/IDAT/,$png);
  my ($crc,$data,$head,@idat,$tail,$raw,$cmp);
  my $size = 0;
  foreach my $d (@data){
    if ($size > 0) {
      push(@idat,substr($d,0,$size));
    }
    if ($size == 0){
      $head = substr($d,0,length($d) - 4);
    }
    $tail = substr($d,($size + 4),(-$size + 4));
    $size = unpack('Na',substr($d,length($d) - 4,4));
  }
  my $x = new Compress::Raw::Zlib::Inflate();
  $x->inflate(join("",@idat), $raw);
  $raw =~ s/a/b/g;
  my $d = new Compress::Raw::Zlib::Deflate();
  $d->deflate($raw, $cmp);
  $size = pack('N',[length($cmp)]);
  $data = $size.'IDAT'.$cmp;
  $crc = pack('N',[crc32($cmp,crc32('IDAT'))]);

  my $glt = $head.$data.$crc.$tail;
  return $glt
}

open(OUTFILE, '>'.$opt_name);
binmode(OUTFILE);

if ($file_name =~ /\.jpe?g$/){
  $buf = &jpeglitch($buf);
}elsif($file_name =~ /\.png$/){
  $buf = &pnglitch($buf);
}


print OUTFILE $buf;