Variants are usually selected from a dropdown menu. However, customers have a tendency to go through product images to find the variant they like, without making a selection from a dropdown. Once they add a product to cart, the initially selected variant will be added, instead of the image that they chose.
With this functionality, Allow your customers to select a product variant by clicking a variant image. This feature is recommended if you have 1 image per variant. If you have multiple images per variants, you can take a look at Display thumbnails connected to the selected variant task.
* An additional take might be needed depending on the theme, if you want it mobile-ready (swiping through images)