How does the scale image option work?

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

You can find these options inside the 'Product image' section, in the Visual preferences.

Just go to the Visual styles section of the app's preferences:

By checking the Scale function for both width and height, you should be able to scale the image to the largest size inside the content area. 

Please note that you can also modify the content area with the options below:

and the product width, inside the 'Product' section, in the Visual preferences:

Please check the related articles to get more insight into these parameters.

If the Image fit function is enabled, some images may appear bigger or smaller than others, like in this screenshot:

If you want the container element always with the same size, you can just disable the Image fit function. 

When you disable this function, the images are as large as possible so that the area is completely covered by the image. Some parts of the image may not be visible in the viewport area.

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