Simply replace the unfilled areas such as "[]" and "[date]" with your information.
Dear [customer],
It was a pleasure to work with you on documenting your [type of event] with professional photographs. I have included the entire photo package you ordered, and feel that you will be pleased with how everything turned out. Please let me know if you have any questions or concerns about the photo package.
Also included is the invoice for the remainder of the payment due. You will note that the amount due has been adjusted by your deposit, and the remaining balance is [total due].
Please remit payment at the address included on the invoice within fifteen days of receipt.
Thank you again for allowing me to take photographs at [type of event].
Sincerely,