I\'ve looked many amazon docs but didn\'t find enough information to upload and download images to S3 using Swift.
How can I do that?
If all you want is to download the image, this is a much more concise and correct way to do it:
func downloadImage(bucketName: String, fileName: String, completion: (image: UIImage?, error: NSError?) -> Void) {
    let transferUtility = AWSS3TransferUtility.defaultS3TransferUtility()
    transferUtility.downloadDataFromBucket(bucketName, key: fileName, expression: nil) { (task, url, data, error) in
        var resultImage: UIImage?
        if let data = data {
            resultImage = UIImage(data: data)
        }
        completion(image: resultImage, error: error)
    }
}