How to generate random names for images that are going to be uploaded?

I'm having trouble creating random names for my images.    I was having the md5 function (mt_rand (1,10000) but I did not succeed using it together with has :: file.

    public function anexar () {
        if(Input::hasFile('file')){
          $file = Input::file('file');
          $file->move('uploads', $file->getClientOriginalName());
          return 'Anexado com sucesso';
          }
        } 
    }