Register a custom payment icon to show on the checkout form.
<?php
/*
 * Plugin Name: Easy Digital Downloads - Custom Payment Icon
 * Description: Register a custom payment icon to show on the checkout form.
 * Author: Easy Digital Downloads
 * Author URI: https://easydigitaldownloads.com/
 * Version: 1.0
 */

function pw_edd_payment_icon( $icons = array() ) {
    $icons['url/to/your/image/icon.png'] = 'Name of the Payment Method';
    return $icons;
}
add_filter( 'edd_accepted_payment_icons', 'pw_edd_payment_icon' );
To implement this snippet on your site, create a brand new, empty WordPress plugin and paste the above code inside.