Zurb TwentyTwenty module is mostly intended to highlight the difference between two images on a Drupal site.
One example use case is advertising images for skin products. Those images present half of the face before applying the product and half of the face after applying it.
Besides doing direct comparisons between images, you can use this module for other purposes as well. In this tutorial, you will learn how Zurb TwentyTwenty module works.