When the photographer sent the photos, he said to send the original pictures first. What is an original work?

This is a photo, without any processing, but the size has been reduced. This small piece is only the original sample for the customer. Because of its low pixel, customers can't enlarge the photos to very satisfactory quality and effect, thus protecting the photographer's shooting and some rights in the later period, and preventing customers from canceling the contract with the photographer after getting the original photos.