$dir="/home/yehuda/img/jpg";

opendir(DH,$dir)or die "FOO BAR! $!\n";

while ( readdir DH)
{
    if ( -f "$dir/$_" && $m/^(.*)\.(.*)\.(.*)/ )
    {
        warn "cannot rename $dir/$_\n"
            unless rename "$dir/$_", "$dir/$1.$3";
    }
}
closedir DH;