#!/usr/bin/env perl

use strict;
use warnings;

my $html_fragment = <<'END_HTML';
    <img src="http://images.google.com/someimage.jpg" />
    <img src="http://images.google.com/NOTsomeimage.jpg" />
    <img src="http://google.somesite.org/image.jpg" />
    <img src="http://somesite.net/google/image.jpg" />
    <img src="http://anythingelse.com/etc.jpg" />
    <img src="http://pictures.google.com/someimage.jpg" />
    <img src="http://google.com/someimage.jpg" />
END_HTML

my $domain_to_keep = 'google.com';

print "Initial markup:\n";
print $html_fragment;

$html_fragment =~ s/\s*<img.*src="http:\/\/(?!.*\Q$domain_to_keep\E\/)[^>]+>//gm;

print "Modified markup:\n";
print $html_fragment;