title: How to update exif of ALAsset without changing the image?
body: <p>I use <code>setImageData:metadata:completionBlock:</code> of <code>ALAsset</code> to update the exif(metadata) of an asset. </p>
  
  <p>I just want to update the metadata, but this method require an <code>imageData</code> as the first parameter. I use the code below to generate <code>imageData</code>, but it modified my image(I checked the file size and file hash).</p>
  
  <pre><code>ALAssetRepresentation *dr = asset.defaultRepresentation;
  UIImage *image = [UIImage imageWithCGImage:dr.fullResolutionImage scale:dr.scale orientation:dr.orientation];
  NSData *data = UIImageJPEGRepresentation(image, 1);
  </code></pre>
  
  <p>Is there any other method I could use to update just the exif of an <code>ALAsset</code>? Or any way to generate the right <code>imageData</code> for method <code>setImageData:metadata:completionBlock:</code> ?</p>