Foundations3 min read
Person ReID vs face recognition vs tracking
Compare person-appearance retrieval, facial recognition and video tracking by input, output, failure mode and governance impact.
Person re-identification, face recognition and tracking are sometimes grouped together as “identity AI”. That shorthand hides major technical and legal differences. Choosing the correct term is the first control against building more capability than a workflow needs.
A compact comparison
| Capability | Typical input | Typical output | What it does not establish |
|---|---|---|---|
| Person ReID | One or more person crops | Ranked appearance-similarity candidates | A civil identity or guaranteed match |
| Face recognition | A visible face plus a reference or enrolled gallery | Facial comparison or identity candidate | Intent, consent or lawful use |
| Tracking | Ordered video frames | A temporary trajectory or track ID | Identity outside the observed sequence |
PolyReID’s API implements only the first row: one crop containing one person becomes a 768-D appearance embedding for similarity retrieval and human review.
Person ReID
Person ReID uses clothing, shape, texture and other appearance cues learned by a model. It is useful when a face is not visible or when a collection is organised around full-body photographs. Its strength is also its limitation: appearance can change, and two people can look alike.
The v1 API has no temporal context, pose estimator, face recogniser, detector or name database. A close vector is a candidate to inspect.
Face recognition
Face recognition focuses on facial features. Depending on design, it can verify a claimed identity or search an enrolled gallery. A ReID embedding is not a substitute for a face template, and adding face recognition changes both the technical system and the privacy analysis.
Do not market an appearance vector as “anonymous” merely because it contains no name. A persistent vector used to single out a person may still be personal or biometric data.
Tracking
Tracking associates observations across adjacent video frames using time, motion and visual continuity. A tracker can maintain a temporary track ID without knowing who the person is. Person ReID may be one signal inside a tracking system, but the PolyReID API does not provide live tracking and its intended purpose is offline photographic retrieval.
Combining components changes the intended purpose. A static embedding service integrated into live surveillance is not equivalent to the documented offline event-photo workflow.
How to choose
Start with the user problem and the minimum necessary signal:
- for finding visually similar authorised photographs, consider Person ReID;
- for continuity inside a bounded video sequence, consider tracking;
- for a facial comparison, assess whether face recognition is necessary and lawful;
- for a simple folder, barcode or consented identifier, do not add biometrics at all.
Then validate on the real domain. Document who reviews results, how errors are corrected, how long vectors remain, and which decisions are forbidden.
For an implementation pattern, read the API integration guide. For the representation layer, continue with embeddings and vector databases.