Progressive JPEG (Legacy IE Alias)

import magic
# Libmagic will correctly identify the file as 'image/jpeg' regardless of the 'pjpeg' extension or legacy IE headers
print(magic.from_file('upload.pjp', mime=True)) # Outputs 'image/jpeg'

// In Express.js (Multer), map pjpeg to jpeg to prevent upload rejection
if (file.mimetype === 'image/jpeg' || file.mimetype === 'image/pjpeg') {
  cb(null, true);
}

import "net/http"
// http.DetectContentType will resolve progressive JPEGs to "image/jpeg", completely ignoring the legacy pjpeg alias.

// Standardize legacy IE uploads in PHP
if ($_FILES['image']['type'] == 'image/pjpeg') {
    $_FILES['image']['type'] = 'image/jpeg';
}