title: How to find corresponding points in two images?
body: <p>I am working with image registration. I am using OpenCV. I have two images I1(reference image), I2(current image). I determine Affine motion between them then warp I1 to see how much it aligns with the current image I2. At this point I have 3 images I1, I1'(distorted) and I2. </p>
  
  <p>Now I need to set 4 points on the current image I2 ( this is for display purpose on a GUI) and need to find corresponding 4 points on the initial reference image I1 (prior to applying the motion). The GUI highlights some feature difference and needs to toggle back and forth on I1 and I2 for the user to understand the difference.</p>
  
  <p>the four points are basically an arbitrary rectangle within the image. For example: </p>
  
  <pre><code>cv::Point P1, P2, P3, P4;
  P1.x = I2.cols / 4;
  P1.y = I2.rows / 4;
  P2.x = I2.cols * 3 / 4;
  P2.y = I2.rows / 4;
  P3.x = I2.cols * 3 / 4;
  P3.y = I2.rows * 3 / 4;
  P4.x = I2.cols / 4;
  P4.y = I2.rows * 3 / 4;
  </code></pre>
  
  <p>I need to find corresponding points of P1, P2, P3, P4 on reference image I1. 
  Any idea on how can I do that using OpenCV? Or any other way? </p>