You can accept any form of payment outside of the system, by using an "offline payment" payment processor as an alternative for checkout. See this example:

Example payment page with 2 alternatives. The descriptive text and the buttons are customizable.

Your offline payment instructions. The photographer is notified when the client clicks on "Accept".

Once an offline payment is received, a single click on Mark order as paid in your admin space will initiate the automated delivery of any licensed image file present in the order.

See also