The Add To Cart button can be customized in several ways. If you want to replace all the add to cart buttons on your site with your own button, you can upload a new set of cart images and specify the location of those images in the Settings panel of Cart66. For more information about this, see the Cart & Checkout documentation.
If you want to use a custom Add to Cart button just for and individual occurrence, you can specify the URL to the image you want to use in the button path ﬁeld. After you enter the URL to the image, you will see the Add to Cart image update in the preview area of the pop-up window.