gistfile1.txt

  //1
  NSDictionary *imageOptions =
  @{
    (NSString *)kCGImageSourceCreateThumbnailFromImageAlways : @YES,
    (NSString *)kCGImageSourceThumbnailMaxPixelSize : [NSNumber numberWithUnsignedInteger:size],
    (NSString *)kCGImageSourceCreateThumbnailWithTransform : @YES,
    };
  CGImageSourceRef src = CGImageSourceCreateWithURL((__bridge CFURLRef)asset.defaultRepresentation.url,
                                                    nil);
  CGImageRef thumbnail = CGImageSourceCreateThumbnailAtIndex(src, 0, (__bridge CFDictionaryRef)imageOptions);
 
  UIImage *image = [UIImage imageWithCGImage:thumbnail];
  CGImageRelease(thumbnail);
  CFRelease(src);
  return image;
  
  //2
  NSDictionary *imageOptions =
  @{
    (NSString *)kCGImageSourceCreateThumbnailFromImageAlways : @YES,
    (NSString *)kCGImageSourceThumbnailMaxPixelSize : [NSNumber numberWithUnsignedInteger:size],
    (NSString *)kCGImageSourceCreateThumbnailWithTransform : @YES,
    };
  CGImageSourceRef src = CGImageSourceCreateWithURL((__bridge CFURLRef)asset.defaultRepresentation.url,
                                                    (__bridge CFDictionaryRef)imageOptions);
  CGImageRef thumbnail = CGImageSourceCreateThumbnailAtIndex(src, 0, (__bridge CFDictionaryRef)imageOptions);
 
  UIImage *image = [UIImage imageWithCGImage:thumbnail];
  CGImageRelease(thumbnail);
  CFRelease(src);
  return image;