title: How to detect subjective image quality
body: <p>For an image-upload tool I want to detect the (subjective) quality of an image automatically, resulting in a rating of the quality.</p>
  
  <p>I have the following idea to realize this heuristically:</p>
  
  <ul>
  <li>Obviously incorporate the resolution into the rating.</li>
  <li>Compress it to JPG (75%), decompress it and compare jpg-size vs. decompressed size to gain a ratio. The blurrier the image is, the higher the ratio.</li>
  </ul>
  
  <p>Obviously my approach would use up a lot of cycles and memory if large images are rated, although this would do in my scenario (fat server, not many uploads), and I could always build in a "short circuit" around the more expensive steps if the image exceeds a certain resolution.</p>
  
  <p>Is there something else I can try, or is there a way to do this more efficiently?</p>