title: pre-processing to find the differences between two images using python opencv
body: <p>In the below attached images, I have to find the differences and point them out in the images labelled as "#-right.png". I had planned to use otsu thresholding and subtraction of images to find out the differences but the problem is the image sizes are not identical (check picture resolutions and the varying borders around the images) for this method to work.</p>
  
  <p>Even if I wanted to use geometrical transformations, I would have to manually point out the points to which the images have to be cropped out (which is different for different images) etc. Is there any way (or any concept I'm unaware of) to make these images identical in resolution so that I can carry on with the subtraction to find the differences?</p>
  
  <p><a href="https://i.stack.imgur.com/4zmDo.png" rel="nofollow noreferrer">7-right image</a>  301x407 px</p>
  
  <p><a href="https://i.stack.imgur.com/iF5cg.png" rel="nofollow noreferrer">7-left image</a>   271x405 px</p>
  
  <p><a href="https://i.stack.imgur.com/0F7dy.png" rel="nofollow noreferrer">1-left image</a>   265x260 px</p>
  
  <p><a href="https://i.stack.imgur.com/n10EP.png" rel="nofollow noreferrer">1-right image</a>  259x264 px</p>