This article applies to Classic Commerce. (Looking for Contextual Commerce documentation?)
When linking from your website to your FastSpring store, button images can compliment the rest of your page, and they stand out better than text links.
Creating Custom Buy Now and Add to Cart Buttons
You can create your own, custom buy now and add to cart buttons using one of the many third-party tools available online. FastSpring does not necessarily recommend or endorse any particular tool or site for button creation, but here is an example of one that might be helpful for you: