sub dummy_ad {
    my $file_ext = lc $_[0];
    if ($file_ext =~ m/gif/) {
        print "$DUMMY_GIF\n";
    } elsif ($file_ext =~ m/jpg|jpeg/) {
        print "$DUMMY_JPG\n";
    } elsif ($file_ext =~ m/png/) {
        print "$DUMMY_PNG\n";
    } else {
        print "$DUMMY_HTM\n";
    }
}