By default, the focal point of an image you add to a banner or snippet is at the centre of the image. Craft allows you to customise this so that regardless of the device the image is being viewed on, the focus point of your image will not be cut off.
Navigate to the entry and locate the image:
Double click the image then select edit (you will need to hover over the image to reveal the edit button)
Select focal point, then look for the white circle in the centre of the image
After you have adjusted the focal point, click save in the bottom right corner