#!/usr/bin/perl -w

use strict;

use CGI qw/:standard/;
use DBI;

my $dbh = DBI->connect("DBI:mysql:database", "user", "password", {RaiseError => 1});

my $sth = $dbh->prepare("SELECT img FROM table WHERE id = ?");
$sth->execute(param('id'));

my $img = $sth->fetchrow_arrayref;

print header("image/jpeg"), $img->[0];