In order to add a photo to a customer we will go to:

Clients --> Clients.

When we see the list of all the clients we will press the "Edit" button of the client we want to add the photo.

When we open the window with all the customer information, we will press the image of the client in the upper left corner.

We have two options, from the icon of the camera, the one on the left, we can make the photo at that same moment if we have a webcam, or from the icon on the right, the folder, we can upload it from our computer.