EXIF (Exchangeable Image File Format)

When a camera writes a JPEG image to storage, it separates visual compressed scanlines from administrative metadata containers using two-byte hexadecimal marker prefixes: 1. JPEG Start of Image (SOI): Marked by `0xFFD8`. 2. APP1 Application Marker: Marked by `0xFFE1`, followed by a 2-byte length indicator. 3. EXIF Header Identification Code: A 6-byte null-terminated ASCII string: `Exif\0\0` (`0x45 0x78 0x69 0x66 0x00 0x00`). 4. TIFF Header (Byte Ordering): • `II` (`0x4949`) specifies Little-Endian (Intel byte order, least significant byte first). • `MM` (`0x4D4D`) specifies Big-Endian (Motorola byte order, most significant byte first). • Followed by the fixed arbitrary identifier `42` (`0x002A`). 5. Image File Directories (IFD): • `IFD0` (Primary Image Metadata): Camera manufacturer, model, orientation, and software version. • `ExifIFD` (Sub-IFD for Photography Attributes): Exposure time, F-number aperture, ISO speed rating, focal length, flash firing state. • `GPS IFD` (Geolocation): Latitude reference (N/S), latitude degrees/minutes/seconds, longitude reference (E/W), longitude coordinates, altitude, and timestamp.

The most critical EXIF metadata tags and their operational relevance:

Because EXIF data introduces both privacy hazards and unnecessary byte payload overhead (often 20 KB to 120 KB per image), production web platforms automatically strip metadata upon ingestion. Here is how modern engineers inspect and strip EXIF using Node.js and browser canvas APIs:

// Method 1: Client-Side Canvas Re-encoding (Zero Dependencies, 100% Privacy)
// Re-drawing an image onto an HTML5 canvas discards all binary APP1 EXIF chunks!
export async function stripExifInBrowser(file) {
  const bitmap = await createImageBitmap(file);
  const canvas = document.createElement('canvas');
  canvas.width = bitmap.width;
  canvas.height = bitmap.height;
  const ctx = canvas.getContext('2d');
  ctx.drawImage(bitmap, 0, 0);

  return new Promise((resolve) => {
    canvas.toBlob((blob) => {
      resolve(new File([blob], file.name.replace(/\.[^/.]+$/, "") + ".clean.jpg", {
        type: 'image/jpeg',
        lastModified: Date.now()
      }));
    }, 'image/jpeg', 0.92);
  });
}

// Method 2: Node.js Sharp Pipeline
// const sharp = require('sharp');
// await sharp('user_upload.jpg').withMetadata({ exif: {} }).toFile('sanitized.jpg'); // clears tags