How to add a reference photo
The reference photo is the enrollment template against which the signer's live face is compared. Pick the right one and verification succeeds smoothly. Pick the wrong one and the signer fails verification — even if they are the right person.
What the reference photo is used for
Before the signing ceremony begins, District Seal computes an ArcFace embedding from the reference photo. That 512-dimensional vector is stored and becomes the ground truth. When the signer completes the ceremony, the server computes an embedding of their live face from the recorded video and compares the two. If the cosine distance between them is below the configured threshold (default 0.55), the identity check passes.
What makes a good reference photo
Face clearly visible
- Front-facing or very near front-facing
- Entire face in frame, forehead to chin
- Eyes clearly visible and open
- No sunglasses, hats, or heavy filters
Good lighting
- Even, front-on light — daylight or a soft lamp
- No strong shadows across the face
- No strong backlighting (window behind the person)
Neutral expression
- Relaxed, mouth closed
- Eyes open, looking at the camera
Recent photo
- Within the last 12 months is ideal
- Current hairstyle and facial hair (a signer who has grown a full beard since the photo was taken may match less reliably)
Plain background
- Any plain wall, curtain, or neutral backdrop works
- No crowd, no other faces in the frame
What to avoid
| Avoid | Why |
|---|---|
| Group photos | Multiple faces confuse the detector. Crop to one face. |
| Side profiles | ArcFace is best at frontal faces. A 3/4 or profile shot will produce a very different embedding. |
| Old photos with different hairstyle or weight | Embeddings shift with significant appearance changes. |
| Heavily filtered photos | Beauty filters change face geometry and reduce match accuracy. |
| Photos with another person's face at any scale | Even a small face in the corner can confuse detection. |
| Screenshots from social media | Often compressed and resized; may have watermarks or text. |
| Low-resolution or blurry images | Detector needs enough pixel detail to localize landmarks. |
Technical requirements
| Property | Requirement |
|---|---|
| File format | JPEG, PNG |
| File size | Under 10 MB |
| Minimum resolution | 400 × 400 px recommended (higher is better) |
| Face proportion | Face should occupy roughly 30–60% of the frame |
How to crop a good reference photo
- Open the photo in any image editor (Preview, Photos, Photoshop, GIMP).
- Crop so the face is centered and takes up most of the frame, with a small margin around the head.
- Do not enlarge or stretch — crop, don't resize.
- Save as JPEG at high quality.
- Upload to the Reference photo drop zone in the New Request view.
Why the reference photo matters for legal defensibility
The reference photo is the anchor of the identity verification. If a signature is later disputed, the certificate and the forensic record show that the person who signed matched this specific reference photo, within this specific threshold, at this specific time. An ambiguous reference photo — a group photo, a blurry shot, a heavily filtered image — weakens the chain of evidence. A clear, recent, front-facing photo strengthens it.
Troubleshooting
| Problem | Fix |
|---|---|
| Signer fails face match even though it's the right person | Reference photo is likely outdated or taken at an angle. Use a recent, front-facing photo. |
| "No face detected" error on upload | The detector could not find a clear face. Crop tighter, improve lighting, remove other faces. |
| Distance came back close to the threshold (0.50–0.55) | Borderline. If the signer can retry with better lighting it may pass. If it fails consistently, replace the reference photo. |
District Seal is a product of NEXSIM LLC, Montana, United States.
Support: support@districtseal.com