You can verify some of them algorithmically, but there are plenty of generators available online which will generate fake credit card details that will pass the

You can verify some of them algorithmically, but there are plenty of generators available online which will generate fake credit card details that will pass these checks. Also it's worth noting that you're not allowed to display the Mastercard/Visa logo without specific permission from them (normally you get this automatically when you get a payment gateway, etc.) If you do have a processor then you can do a pre-authorization credit check (does this person have the money to pay for it?) without actually charging them.