codeigniter how to upload picture to folder, web/assets/picture/

i am using codeigniter i want to upload a file picture to my folder, path is web/assets/picture/

ive look up here and cannot fix with the answer i found. please help.

this my view where to input the picture :

echo form_open_multipart("adminFolder/admin/insert_picture");   
echo form_upload("userfile", "Gambar Picture"); 
echo form_submit("input_picture", "Input now !!!");

my controller the insert_picture :

        if($this->input->post("userfile")){
            $this->model_get->doUpload();

            $this->adminPic();
        }else{
            $this->insertPicture();
        }

my model :

function doUpload(){

        $config['upload_path'] = '../assets/images/'; 
        $config['allowed_types'] = 'gif|jpg|png|jpeg'; 
        $config['max_size'] = '2048'; 
        $config['max_width']  = '1024';
        $config['max_height']  = '768'; 
        $config['overwrite'] = TRUE;

        $this->load->library("upload", $config);
        $this->upload->do_upload();

    }