Name and Search People
Photos performs 11 billion computations on every photo to analyze its contents for faces, scenes, and objects. But while Photos is good at recognizing faces, it’s terrible at putting names to those faces. Unless you’ve been diligent about adding everyone whose picture you take to the Contacts app (complete with a picture that Photos can use to identify them), you need to do some work in the People album (Figure 43), located in the Library section of the sidebar on a Mac and in the People & Places section of the Albums view on an iPhone or iPad, to teach Photos who’s who.
Find All Photos for a Person
The People album contains all the faces Photos has identified and connected to a name. If you want to find photos of a specific person, this is the place to go—just select an item to see all the photos that Photos has matched to that face. You also find a map showing all the places where photos of this person were taken, a list of other people who are frequently seen with this person, and even automatically-generated Memories (see Unearth Old Photos with Memories) that this person appears in (Figure 44).
Having your photos tagged based on who’s in them is a great organizational tool. For example, when it’s time to find photos of my family for our holiday cards and annual calendars, I can use a smart album on a Mac that displays photos containing all four of our faces (see Define Smart Albums on a Mac) or just search for all for of us (see Embrace the Search Box). It’s sobering to discover that in a full year, you were photographed with your family only a handful of times.
Name and Merge People
Apple’s face recognition engine is really good at finding faces. Of course, it doesn’t know who most of those people are, and you’ll find that the same people are listed multiple times. It takes a little work to get your People list in order, though every move you make helps the face recognition engine learn and improve so that it’s better at matching other faces across all your devices.
To associate a name with an unnamed face in the People view, move the pointer over the face and click Unnamed. Then begin to type that person’s name.
As you type, a pop-up menu suggests people Photos already knows about via its own catalog of faces or your Contacts app (Figure 45). If one of those is the person you’re looking for, select it. Otherwise, just type the person’s name and press Return.
If the full name you assign is already represented in the People album, both sets of photos can be merged together. To merge faces together, just drag one face tile on top of another (Figure 46).
Assign People Manually
Unfortunately, the vast mass of faces in your photos will be unlabeled. You can assign names to faces directly in the single-photo view, which can help if you just know you have pictures of somebody but they don’t show up in your People album at all.
On a Mac, face detection is, well, right in your face: When you are in single-photo view, you see labels floating above the photo, either containing names or the word Unnamed. (If you don’t see these hints, turn them on by choosing View > Show Face Names.) When you move the pointer over faces associated with those labels, you see circles indicating the area where the face was detected. You can click those labels and enter the name of the person, which makes them appear in the People album if they weren’t there already (Figure 47).
On an iPhone or iPad, adding a person is a bit less direct. From the single-photo view, scroll down to reveal more information about the photo, including a People section. If faces were detected in an image, they appear in circles within the People section (Figure 48). Tap one of the faces and you see a screen containing the instances of that face found in your library. Tap Add Name to put a name to the face, and they are added to your People album.
Identify More People
Face recognition is not an exact science. Photos assigns faces it can recognize with a high degree of accuracy, but there’s a muddy middle where it can’t be sure if it’s seeing the right person. This is where you come in. Occasionally when you visit a person’s page within the People album, you are prompted by a banner that says “There are additional photos for review.” You’re being asked to confirm that some faces are actually who Photos thinks they are. If you agree to review the photos, Photos displays up to nine cropped images that focus on the face in question, and give you the option to verify or reject the matches by checking or unchecking each one (Figure 49). This data is fed back into the image-recognition engine, making more matches and assigning even more photos to that person.
If you’re in the mood to help out the face-recognition even more—and when you’re starting out, it can be an enormous help in building up a library of matches—you can see if there are even more provisional face-recognition matches for a person. On a Mac, scroll down to the bottom of any person’s page in the People album and click Confirm Additional Photos. On iOS, tap the More 
icon and choose Confirm Additional Photos.
If there are more photos to be identified, you’re shown them one by one, with the relevant face circled, and asked to identify if this is the person Photos thinks it is. Choose Yes or No, and as you do, Photos indicates how many additional images have been added to that person’s album (Figure 50).
Delete Face Data Entirely
So what if you’ve screwed up your face data? Perhaps you assigned someone the wrong name, or merged a bunch of different faces together? Don’t despair. This happened to a friend of mine, and he found out that there is a solution that lets you start over from the very beginning.
It’s pretty simple: On a Mac, click the People view and press ⌘-A to select every single person in your library. Then press Delete. Photos asks you if you want to “Reset [the] People Album.” This lets you declare bankruptcy on face training and start again from scratch.