title: How to draw circles with random colors in OpenCV
body: <p>I am using SURF algorithm to match two images with OpenCV. 
  And I have got the keypioints.</p>
  
  <p>Now I want to draw these keypoints with random colors circles.</p>
  
  <p>I know how to draw a circle in OpenCV with the function cvCircle, but the color is fixed with <code>cvScalar(r,g,b)</code>.</p>
  
  <p>I want the the color of the circle of a keypoint in a image is different to the circles near it.</p>
  
  <p>The library function <code>cv::drawMatches()</code> in OpenCV have the effect I want. But I don't know how to realize it.</p>
  
  <p>Does anyone who can tell me how to draw the circles.</p>
  
  <p>Thanks!</p>