app\models\Beatmapset::coverURL PHP Method

    public function coverURL($coverSize = 'cover')
    {
        if (!self::isValidCoverSize($coverSize)) {
            return false;
        }
        $timestamp = 0;
        if ($this->cover_updated_at) {
            $timestamp = $this->cover_updated_at->format('U');
        }
        return $this->storage()->url($this->coverPath() . "{$coverSize}.jpg?{$timestamp}");
    }