docs/API.md

# Visa Photo Maker Documentation

## Overview
Visa Photo Maker is a privacy-first, bilingual web application that automatically processes user-uploaded photos into standard visa/passport photo formats. It uses AI to remove backgrounds and intelligently crops the image to meet specific aspect ratios and composition requirements.

## Privacy & Security
**Does the server keep my photos?**
**NO.** 
- Images are processed in **RAM (Memory)** only.
- The backend receives the file -> Removes Background -> Crops -> Returns the result immediately.
- No `save()` to disk operations are performed for user images.
- Once the request is finished, the data is discarded by the server's garbage collector.

## Features
- **AI Background Removal:** Uses `rembg` (U2-Net) to remove complex backgrounds.
- **Smart Cropping:** 
  - Automatically detects the subject.
  - Cleans up semi-transparent noise.
  - Crops excess body parts for correct head-to-body ratios.
  - Ensures no white borders ("Cover Mode").
- **Internationalization (i18n):**
  - Full support for 6 languages:
    - 🇨🇳 Chinese (ZH)
    - 🇺🇸 English (EN)
    - 🇪🇸 Spanish (ES)
    - 🇫🇷 French (FR)
    - 🇯🇵 Japanese (JA)
    - 🇰🇷 Korean (KO)
  - Dedicated SEO-friendly routes (e.g., `/es`, `/ja`).
- **Multi-Standard Support:**
  - US/India: 2x2 inch (600x600 px)
  - Europe/UK/China: 35x45 mm
  - Japan: 30x40 mm
  - Canada: 50x70 mm
- **Queue System:** Strict "One at a time" processing to protect server resources.

## API Reference

### `POST /process-image`

Uploads an image and returns the processed JPEG.

**Parameters (Form Data):**
- `file`: The image file (JPG/PNG).
- `width`: Target width in pixels (e.g., 600).
- `height`: Target height in pixels (e.g., 600).

**Response:**
- Returns a binary JPEG stream of the processed image.

**Concurrency:**
- The server implements a **Global Lock**.
- Only **1 request** is processed at a time.
- Subsequent requests will wait in a queue until the lock is released.

## Architecture
- **Frontend:** Next.js (React) on Port 3000.
  - Components: `src/components/VisaPhotoMaker.tsx` (Core Logic).
  - Routes: `src/app/[lang]/page.tsx`.
- **Backend:** FastAPI (Python) on Port 13002.
- **Process Management:** PM2.

## Deployment
Managed via PM2:
```bash
pm2 list
pm2 restart visa-backend
pm2 restart visa-frontend
```