Swift 4.2 | Xcode 10

extension UIImage {

    /// EZSE: Returns base64 string
    public var base64: String {
        return self.jpegData(compressionQuality: 1.0)!.base64EncodedString()
    }
}

@implementation UIImage (Extended)

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

@end

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

See my class -  AppExtension.swift


// MARK: - UIImage (Base64 Encoding)

public enum ImageFormat {
    case PNG
    case JPEG(CGFloat)
}

extension UIImage {

    public func base64(format: ImageFormat) -> String {
        var imageData: NSData
        switch format {
        case .PNG: imageData = UIImagePNGRepresentation(self)
        case .JPEG(let compression): imageData = UIImageJPEGRepresentation(self, compression)
        }
        return imageData.base64EncodedStringWithOptions(.allZeros)
    }
}

Swift 3.0和Xcode 8.0

let imageData = UIImageJPEGRepresentation(imageView.image!, 1)

    let base64String = (imageData! as Data).base64EncodedString(options: NSData.Base64EncodingOptions(rawValue: 0))
    print(base64String)

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];