How can I hide the AMEX and Discover Logos?

This code worked...

add_filter("gform_creditcard_types", "remove_amex");
function remove_amex($cards){
    unset($cards[0]); // Removes AMEX from the list.
    return $cards;
}

add_filter("gform_creditcard_types", "remove_discover");
function remove_discover($cards){
    unset($cards[1]); // Removes Discover from the list.
    return $cards;
}

You can edit that code as you see fit, but using that code in my themes function.php file I was able to remove AMEX and Discover cards from the 'accepted' card types. The system was smart enough to remove the card logos from the payment form as well.

So, problem solved, just thought I'd share the solution for anyone who runs across the same problem.