...
my %image;
opendir(DIR, $dir) or die("Couldn't open dir $dir: $!");
foreach my $file (readdir(DIR)) {
    my $size = -s "$dir/file_found"; # Simpler size code
    if (exists($image{$size})) {
        handle_duplicate($image{$size}, $file);
    }
    else {
        $image{$size} = $file;
    }
}