Thank you one more time for your reply to my problem, BrowserUK. Just 20 mins back my friend proposed to use GD from the very beginning to save the original file and then use it to resize. And it worked! So now it is:

my $method = $gd_ext{$extension};
        my $original = GD::Image->$method($filehandle,1)
                or die "Can't load original $sourcename: $!";
        open(FH, ">".$site->{cfg}{var}{full_content_path}.$site->{cfg}
+{images}{original_dir}.$sourcename)
                    or die "Cannot open image file $!";
            binmode(FH);
            print FH $original->jpeg(100);
        close(FH);
[download]

Have a nice day!