Deliberately corrupt a JPEG file.

j0rrupt0r.pl

#!/usr/bin/perl -w
use strict;
use Getopt::Std;

# Deliberately corrupt a JPEG file.
#
# ./j0rrupt0r.pl -i nice.jpg -o corrupt.jpg

# Initial fraction of the image that won't be considered
# for corruption (1/fraction)
my $fraction = 3;

# Every how many bytes to consider corruption
my $consider = 757;

# With a probability of 1/$probability, skip a byte
my $probability = 3;


my %opts;
my $fh_in;
my $fh_out;

getopts('i:o:', \%opts);

# Open input and output file
die "Specify input file with -i.\n" unless ($opts{'i'} and (open $fh_in, "<$opts{'i'}"));
die "Specify output file with -o.\n" unless ($opts{'o'} and (open $fh_out, ">$opts{'o'}"));

# Leave 1/$fraction of the image intact before vandalizing
my $size = (stat($opts{'i'}))[7];
my $offset = int($size / $fraction);

my $data;
my $bytes;
for (0..$offset){
        $bytes++;
        read ($fh_in, $data, 1);
        print $fh_out $data;
}

while(read($fh_in, $data, 1)){
        # consider every nth byte for deliberate corruption
        if (0 == $bytes++ % $consider){
                if (0 == int(rand($probability))){
                        # Skip this byte
                        next;
                }
        }
        print $fh_out $data;
}

close $fh_in;
close $fh_out;