When Facebook imports the images of your products, by default it will take a 600x600px crop of the centre of your primary product image. This may not be ideal, especially if your product images are large in size or not in a square aspect ratio.
This option resizes the images first to ensure it doesn’t get cropped. Be aware that images that are significantly taller than they are wide (or vice versa) will be squished to fit a maximum of 600px for the greatest side so they may not be ideal.
To combat this, we advise that you use product images on Shopify that are square or as close to a 1:1 aspect ratio as possible to be suitable in all advertising placements.
Facebook also allows you to change the image cropping settings for each catalog. You can view these settings by going to https://www.facebook.com/products and choosing your catalog. Then select “Settings” from the left menu, scroll down to “Image Cropping” and click “edit”.