Get image url from model good practice?

I think a good start would be OOP, so I started:

PHP Code:

class Product
{

    private $_product;
    private $_resolution;

    public function __construct($product, $resolution){

        $this->_product = $product;
        $this->_resolution = $resolution;
    }

    public function products() {

        foreach($this->_product as $product){
            $product->nume_imagine = $this->parse_image_name($product);
        }

        return $this->_product;

    }


    public function product() {

        $this->_product->nume_imagine = $this->parse_image_name($this->_product);

        return $this->_product;

    }


    private function parse_image_name($product)
    {
        if($product->nume_imagine):
            return base_url('assets/uploads/'.$product->id_produs.'/'.$this->image_resolution($product->nume_imagine, $this->_resolution));
        else:
            return base_url('assets/images/no-product-image-available.png');
        endif;
    }

    private function image_resolution($image_name, $resolution) {

        $image = explode('.', $image_name);
        return $image[0].'_'.$resolution.'.'.$image[1];
    }
} 


The problem is I dont't know where to call and how to call. In model? In controller?