Face Detector / Minor Guard (FastAPI)

This service accepts an image, detects faces, and performs an age check.
If the photo likely contains a minor (<18) — the request is blocked.

Supported age-check providers:

• opencv — local (OpenCV DNN, no cloud)
• aws — AWS Rekognition
• sightengine — Sightengine
• hive — Hive

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Features

• Request ID per request (X-Request-Id), propagated to logs as rid=....
• Unified response format for both success and errors.
• Fail-closed or fail-open behavior when a provider fails.
• Face required: if no face is detected, the request returns an error (cannot verify age).

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Run locally

Install dependencies

python -m venv venv
source venv/bin/activate
pip install -r requirements.txt

Configuration (env vars)

Minimal for OpenCV

Create .env file in the project root.

Use .env.example as a template.

OpenCV tuning

OPENCV_MODEL_DIR=models/opencv
OPENCV_DOWNLOAD_MODELS=true
OPENCV_FACE_CONF_TH=0.7

# IMPORTANT: these are the model's FIXED buckets.
# Use exactly these strings:
# (0-3),(4-7),(8-12),(13-20),(21-32),(33-43),(44-53),(54-100)
OPENCV_BLOCK_BUCKETS='(0-3),(4-7),(8-12),(13-20)'

Start the server

uvicorn server.main:app --reload --host 0.0.0.0 --port 8000

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OpenCV models

On first run, the opencv provider automatically downloads models into models/opencv.

If you ever end up with broken weights / HTML downloaded instead of real models, delete the folder:

rm -rf models/opencv

Then restart the service to re-download clean models.

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Request ID

• Client can send: X-Request-Id: <your-id>
• Service always returns X-Request-Id and includes request_id in JSON responses.
• Logs include rid=<request_id> for easy tracing.

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API

Health

• GET /healthz

Image check

• POST /api/v1/check_image
• multipart/form-data, file field name: file

Example:

curl -s -X POST \
  -F "file=@./photo.jpg" \
  http://127.0.0.1:8000/api/v1/check_image | jq

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Response codes

• 200 OK — check passed
• 403 MINOR_DETECTED — likely contains a minor
• 422 FACE_NOT_DETECTED — no face detected (age cannot be verified)
• 503 AGE_CHECK_UNAVAILABLE — provider is unavailable and fail-closed is enabled

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Unified response format

Success:

{
  "ok": true,
  "request_id": "ef3adfc22947",
  "data": { "filename": "photo.jpg" },
  "minor_guard": {
    "provider": "opencv_caffe",
    "is_minor": false,
    "reasons": ["faces_detected=1", "face[0] age_bucket=(25-32) p=0.81"]
  }
}

Error:

{
  "ok": false,
  "request_id": "ef3adfc22947",
  "data": {},
  "error": "FACE_NOT_DETECTED",
  "message": "No face detected in the image. Please upload a clear face photo.",
  "minor_guard": {
    "provider": "opencv_caffe",
    "is_minor": false,
    "reasons": ["no_faces_detected"]
  }
}

Notes:

• request_id matches the X-Request-Id header (generated if not provided).
• minor_guard.reasons is intentionally capped (keeps payload small).