@implementation UIImage (Extended)

- (NSString *)base64String {
    NSData * data = [UIImagePNGRepresentation(self) base64EncodedDataWithOptions:NSDataBase64Encoding64CharacterLineLength];
    return [NSString stringWithUTF8String:[data bytes]];
}

@end

对于iOS 7+， Objective-C，下面是如何从一个图像URL开始转换:

NSURL *url = [NSURL URLWithString:self.groove.thumbnailURL];

UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:url]];

NSString *base64String = [UIImagePNGRepresentation(image)
base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];

我尝试了所有的解决方案，没有一个对我有效(使用Swift 4)，这是对我有效的解决方案，如果将来有人面临同样的问题。

let temp = base64String.components(separatedBy: ",")
let dataDecoded : Data = Data(base64Encoded: temp[1], options: 
 .ignoreUnknownCharacters)!
let decodedimage = UIImage(data: dataDecoded)

yourImage.image = decodedimage

//convert Image to Base64 (Encoding)

let strBase64 = imageData.base64EncodedString(options: .lineLength64Characters)

print(strBase64)

// convert Base64 to Image (Decoding)

let dataDecoded:NSData = NSData(base64EncodedString: strBase64, options: NSDataBase64DecodingOptions(rawValue: 0))!

let decodedimage:UIImage = UIImage(data: dataDecoded)!

print(decodedimage)

yourImageView.image = decodedimage

在Swift 3.0和Xcode 8.0

编码:

let userImage:UIImage = UIImage(named: "Your-Image_name")!
let imageData:NSData = UIImagePNGRepresentation(userImage)! as NSData
let dataImage = imageData.base64EncodedString(options: .lineLength64Characters)

解码:

let imageData = dataImage
let dataDecode:NSData = NSData(base64Encoded: imageData!, options:.ignoreUnknownCharacters)!
let avatarImage:UIImage = UIImage(data: dataDecode as Data)!
yourImageView.image = avatarImage

斯威夫特iOS8

// prgm mark ---- 

// convert images into base64 and keep them into string

func convertImageToBase64(image: UIImage) -> String {

    var imageData = UIImagePNGRepresentation(image)
    let base64String = imageData.base64EncodedStringWithOptions(.allZeros)

    return base64String

}// end convertImageToBase64


// prgm mark ----

// convert images into base64 and keep them into string

func convertBase64ToImage(base64String: String) -> UIImage {

    let decodedData = NSData(base64EncodedString: base64String, options: NSDataBase64DecodingOptions(rawValue: 0) )

    var decodedimage = UIImage(data: decodedData!)

    return decodedimage!

}// end convertBase64ToImage