Start with a baseline: take front, top, crown, hairline and part photos under repeatable lighting and from repeatable angles.
Keep the conditions similar: use comparable hair dryness, styling, parting and camera distance whenever you repeat photos.
Repeat on a schedule rather than every day. Monthly comparisons are usually easier to interpret than constant checking.
Record context that could affect interpretation, such as haircut changes, new styling, illness, major stress, medication changes, supplements or other hair treatments.
Separate appearance from cause. A photo can show that something looks different; it cannot establish why it changed.
Seek professional evaluation for sudden, rapid, patchy or symptomatic changes instead of relying only on self-tracking.