Magento Go resizes product images according to the dimensions specified by the theme. As a best practice, you should standardize the size of your images to ensure that they appear at the highest possible resolution, and maintain the correct proportion. Using images of various sizes and dimensions can impact the presentation of your product catalog. A good rule to remember is to never resize an image larger than the original. You can always make an image smaller without losing resolution, but not larger.
The Catalog Images tool lets you override the default size and proportion of any image in your catalog layout by specifying the new size in pixels. For example, you can change the size of the images that appear in the “New Products“ block on the Home page, or those that are listed on Category page, or any other catalog image that is displayed in your store.
Each image has three types: A base image, a small image, and a thumbnail. If you specify a new size for the base image, the associated small image and thumbnail are resized automatically. The change applies to any product image that appears at that location in your catalog.
To learn more about resizing catalog images, see the following articles: