That isn't going to be useful. the md5 algorithm is expressly design to detect differences, not similarity:

use Digest::MD5 qw[md5_hex];
my $s = 'the quick brown fox jumps over the lazy dog';
print md5_hex $s;
77add1d5f41223d5582fca736a5cb335

print md5_hex $s . 's';
5e48a737eaff799917707b2815af10fc

print md5_hex $s . 'S';
d02763729a741eed14417a1051ec228c
[download]

Even the addition of a single character, or changing a single bit produces a (numerically) completely unrelated digest--exactly as it should for the purposes for which md5 is designed, but completely wrong for this application.