' alone is 38+ bytes),
// which is exactly how this project's exported SVGs are written - they were
// silently falling through to application/octet-stream, which browsers won't
// render as an <img>.
$bytes = file_get_contents($file, false, null, 0, 512);
$type = 'application/octet-stream';
$ext = strtolower(pathinfo($file, PATHINFO_EXTENSION));
$bytesString = (string) $bytes;
if ($ext === 'svg' || strpos(ltrim($bytesString), '<svg') === 0 || strpos($bytesString, '<svg') !== false) {
  $type = 'image/svg+xml';
} elseif (substr($bytesString, 0, 4) === "\x89PNG") {
  $type = 'image/png';
} elseif (substr($bytesString, 0, 3) === "\xFF\xD8\xFF") {
  $type = 'image/jpeg';
} elseif (substr($bytesString, 0, 4) === 'RIFF' && substr($bytesString, 8, 4) === 'WEBP') {
  $type = 'image/webp';
} elseif ($ext === 'ico') {
  $type = 'image/x-icon';
}

header('Content-Type: ' . $type);
header('Cache-Control: public, max-age=31536000, immutable');
readfile($file);