If you are going to be selecting only one image type at a time, you can add a where clause to the with() method:

$imageTypeId = 'some id you need to set';

$product = Product::with(['images' => function($query) use ($imageTypeId)
{
    $query->where('id_imagetype', $imageTypeId);
}])->where('id_product', '=', Request::segment(2))->get();

If you are going to be loading a product with both image types, but you want them grouped together by type, it's probably better to do something like this:

class Product extends Eloquent {
        protected $table = 'products';

        public function layoutImages() 
        {
            return $this->hasMany('Productimages', 'id_product')->where('id_imagetype', 1);
        }

        public function contentImages() 
        {
            return $this->hasMany('Productimages', 'id_product')->where('id_imagetype', 2);
        }
}

$product = Product::with(['layoutImages', 'contentImages'])->where('id_product', '=', Request::segment(2))->get();