How to classify images based on a small region of the images

I am trying to build a NN that classifies corona rapid test kits based on their result (positive, negative). I am curious if there is a common way to focus the NN on the small window of the test kits, which determines the result of the corona rapid test. Cut out irrelevant parts of the images and only focus on the small window with stripes next to C and T.

Is a Region of Interest layer the correct approach?

deeplearning images small