title: Detect presence/absence of a ball in image
body: <p>What are best methods/techniques I can use to detect the presence/absence of a ball in an image?  I'm using grayscale cameras and am trying to prevent my Circle Hough Transform from producing false positives when there is no ball present in the scene.  </p>
  
  <p>Would it possible to achieve this using the average grayscale value of the scene and detecting an increase in this average value to detect the presence of a ball?</p>
  
  <p>Many thanks everyone for your inputs in advance.</p>