How does the fit image option work?

Frequently Bought Together has an option to fit the image to the container element leaving the browser the responsibility to scale it appropriately.

You can find that option in the Visual Preferences section from app preferences page, by cliking on the product image icon in the visual selector on the left:

By checking the Product image fit option all images will be enclosed in its container, so both its width and its height fit inside the content area. Please note that you can also modify the content area with the options below:

The related article describes these functions with more details.

If the Product image fit option is enabled some images may be displayed bigger or smaller than others, like in this screenshot:

To make all images look similar you can just disable the Product image fit option. When you disable this option the images will be as large as possible so that the area is completely covered by the image.Some parts of the image may not be in view within the positioning area. 

In this case here is how the widget will look like with disabled Product image fit function: