swift

    let image = UIImage.init(named: "1024-01")
            /// t图片转data
    let data = UIImagePNGRepresentation(image!)
    // data 转string 注意是base64EncodedStringWithOptions 这个方法不能使用         [NSString.init(data: <#T##NSData#>, encoding: <#T##UInt#>)] 必须是这个编码

    let str = data?.base64EncodedStringWithOptions(.Encoding64CharacterLineLength)

    // string转data
    
    let data1 = NSData(base64EncodedString:str!,options: .IgnoreUnknownCharacters)
    // data 转 图片
    let image2 = UIImage.init(data: data1!)
    
    print(image2)

oc

UIImage *image = [UIImage imageNamed:@"640"];
NSData *data = UIImagePNGRepresentation(image);
NSString *str = [data base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];

NSLog(@"%@",str);


NSData *data1 = [[NSData alloc] initWithBase64EncodedString:str options:NSDataBase64DecodingIgnoreUnknownCharacters];
UIImage *image1 = [[UIImage alloc] initWithData:data1];
NSLog(@"%@",image1);