IOS图片转base64字符串和字符串转回图片

    UIImage图片转成base64字符串：

UIImage *_originImage = [UIImage imageNamed:@"temp.png"];

NSData *_data = UIImageJPEGRepresentation(_image, 1.0f);

NSString *_encodedImageStr = [_data base64Encoding];

Base64字符串转UIImage图片：
NSData *decodedData = [[NSData alloc] initWithBase64EncodedString:base64String options:0];

UIImage *_decodedImage      = [UIImage imageWithData:_decodedImageData];

NSLog(@"===Decoded image size: %@", NSStringFromCGSize(_decodedImage.size));