// 1. default use SKPhoto
    var images = [SKPhoto]()
    for url in urls {
        let photo = SKPhoto.photoWithImageURL(url)
        photo.shouldCachePhotoURLImage = true // you can use image cache by true(NSCache)
        images.append(photo)
    }

    // 2. use KFPhoto by SKPhotoBrowser-Kingfisher
    var images = [KFPhoto]()
    for (index, url) in urls.enumerated() {
        let holder = ImageCache.default.retrieveImageInDiskCache(forKey: middlePics[index])
        let photo = KFPhoto(url: url, holder: holder)
        images.append(photo)
    }