Can I add credit card icons to payment method

I can see you're using Square as payment gateway, unfortunately there is no a way to set the Credit Card icons from the settings; however, you may add them at the bottom of the field by injecting this CSS code: 

[data-type="control_square"] table.form-address-table::after {

    content: "";

    width: 180px;

    height: 25px;

    background: no-repeat;

    position: absolute;

    background-image: url("https://cdn.jotfor.ms/images/credit-card-logo.png");

}

You can also replace the "background-image" link with the link to your custom image and also do note that the "width" and "height" properties may need to be changed if you change the image used. 

Here is how the result should look like: 

This guide will help you to inject the code to your form: How-to-Inject-Custom-CSS-Codes

Hope this helps.