Facial recognition

Without facial recognition, the app finds a person again by their clothing. Facial recognition goes further: it compares faces, so it can find someone after they change their jacket, put on a hat, or appear on another day. You can also search with a photo of the person.

It only compares faces in your own footage and the photos you add. It does not look anyone up or tell you who a person is. Everything happens on your computer, and it is free.

Why it's off until you turn it on

A face is personal data in a way that clothing is not, and the rules for using it are stricter. Some US states, such as Illinois, Texas and Washington, have laws about it; some cities and agencies limit it; and clients and courts may ask how a face match was made. So the app is careful:

• It's off until someone chooses to turn it on. The account owner turns it on and signs their name to do it.
• It keeps a record. Who turned it on or off and when, and every face search: who ran it, when, and what they looked at. If a match is ever questioned, you can show how it was made.
• Nothing leaves your computer. No face or photo is sent anywhere.
• Turning it off deletes the faces. You never hold face data you aren't using.
• You make every decision. A match only counts when you click Same, and the report says so.

Turn it on

1. Go to Settings → Analysis and find Faces.
2. Click the switch. Read the screen that explains the rules, tick the box, type your full name, and click Turn on Faces.
3. The app looks for faces in the open case straight away, and tells you when it's done.

Use it

Open an event, click the person, click Find more, and switch from Clothing to Face at the top. To search with a photo instead, click Subjects → Find by photo and choose the photo.

Which faces work

The face needs to be fairly large in the picture — about 40 pixels across — and facing the camera. Close cameras, like a front door or an entrance, work well. Wide views of a street or driveway usually don't. Settings → Analysis → Faces shows, for each file, how many people had a usable face.