After you have registered a product, you will see that it now automatically gets an avatar that represents its category. This image also becomes visible in the configuration items that you register based on the product. You can still overwrite this avatar by uploading a picture of the product, but perhaps you prefer to simply leave it set to the default image.
Below are a few examples of default product category avatars:
Software license certificates are treated a little differently. For them, a special image gets presented regardless of the product that it is linked to. That makes it easier to differentiate them from the software CIs.