For the past couple of years, I’ve been writing automated tests for my employer. One of the many types of tests that I do is comparing how an application draws. Does it draw the same way every single time? If not, then we have a serious problem. An easy way to check that it draws the same each time is to take a screenshot and then compare it to future versions of the same drawing when the application gets updated.
The Pillow library provides a handy tool for this sort of thing that is called ImageChops. If you don’t already have Pillow, you should go install it now so you can follow along with this short tutorial.
Comparing Two Images
The first thing we need to do is find two images that are slightly different. You can create your own by using burst mode on your camera and taking a bunch of photos of animals as they move, preferably while using a tripod. Or you can take an existing photo and just add some kind of overlay, such as text. I’m going to go with the latter method. Here is my original photo of Multnomah Falls in Oregon: