Why compare photos?
One photo of a hairline tells you its shape today. It cannot tell you whether the hairline is moving, and that is usually the question. A mature hairline steps back a little at the temples and then holds. A receding hairline keeps moving. The two can look the same in a single photo and different a year apart, which is why comparing two photos is the useful test.
This tool does the comparison for you. It runs in your browser, both photos are read on your device and never uploaded, and the result is a cosmetic estimate from two photos.
How the hairline comparison works
When you add a photo, two small models download to your browser. A face landmark model finds your brow line, the point between your brows, the base of your nose and the outer corner of each eye. A hair model marks which parts of the photo are hair. The tool then walks up your forehead in 45 columns and records where hair starts in each, which gives your traced hairline. It does this for both photos.
To put the two hairlines on one photo, the tool shifts, turns and resizes the earlier hairline so that the outer corners of your eyes sit where they do in the recent photo. Your eyes are a steadier reference between photos than your hairline is. It then draws the earlier line, dashed, over your recent photo. A gap between the two lines is a change.
Distances are measured in mid-face units: the distance from the point between your brows to the base of your nose. Because the unit comes from your own face, the camera, the distance and the size of the photo do not change the result.
The models were made by Google’s MediaPipe team for photo effects and augmented reality, not for medical use.
How big a change counts?
Two photos of the same hairline never measure exactly the same. Light, camera angle and how your hair is pushed back all move the result a little, so a small difference is not a change.
The tool reads each photo three times, from slightly different crops, and looks at how much those three readings disagree. That gives it an estimate of the normal difference for each photo. A change only counts when it is bigger than that, and never smaller than a fixed floor.
| What the tool checks | How it decides, in mid-face units |
|---|---|
| A change in hairline height or temple depth | It counts when it is at least 0.06, or the readings’ own disagreement if that is larger |
| Photos taken at different angles | The lower thirds of the two faces differ by more than 0.2 |
These numbers are ours, written for this tool. They are rules of thumb and not a clinical standard. If a change is under the line, the tool says there is no clear change, which means the two photos cannot be told apart. That is a useful answer.
How to take photos that compare fairly
The more alike the two photos are, the more the result means. Take them the same way every time.
- Push your hair straight back the same way, or tie it back, and take off hats and headbands.
- Face the camera straight on, with it at eye level and about an arm’s length away.
- Keep your eyebrows relaxed. Raising them changes how high the hairline looks.
- Use bright, even light from the front, in the same place if you can.
- Wait months between photos. Three to six months is a sensible gap, and a few weeks is too short to see a real change.
If you are starting now, take a photo today and save it somewhere you will find it. In a few months you will have your “earlier” photo.
What the result means
The tool reports two things separately.
- Hairline height: whether the middle of your hairline sits higher or lower in the recent photo.
- Temples: whether your temples sit further back from the middle of your hairline than they did.
Temples moving back is the change most worth noticing, because it is the pattern hereditary hair loss often starts with. The American Academy of Dermatology notes that in men, the first sign of hereditary hair loss is often a receding hairline or a bald spot at the top of the head. A change that is bigger than the noise is a reason to repeat the comparison with a fresh pair of photos, and to talk to a doctor if it keeps showing up or if you are worried.
Our guide to mature and receding hairlines goes through the signs.
What two photos cannot tell you
Two photos show that a difference exists. They do not show why, how fast it is moving or what is happening at your crown. They are not a diagnosis. See a doctor or dermatologist if hair loss is sudden or patchy, if your scalp is itchy, red, scaly or sore, or if your eyebrows or eyelashes are thinning too.
Let the HairLens app line them up for you
The HairLens app keeps every scan, lines them up month after month and charts the trend, with a monthly report of what changed and what stayed the same, so you never have to find and match old photos yourself.