With Photos for OS X, changing the image that Faces uses for a person in the album screen has been tweaked slightly from its iPhoto days. Here's how to go about it.

How to change Faces key photos in Photos for OS X

  1. Open Photos for OS X and navigate to the Albums section, then select Faces.

  2. Select the Face whose photo you want to change and open the sub-album.

  3. Find the photo you want to use, and control-click (or right-click) on it, then select Make Key Photo.

Photos for Mac