gistfile1.txt

$imgData = file_get_contents($path);

// determine mime type
$magicNumbersToMimeTypes = array(
  '474946383761'=>'image/gif',     // GIF87a type gif
  '474946383961'=>'image/gif',     // GIF89a type gif
  '89504E470D0A1A0A'=>'image/png', // png
  'FFD8FFE0'=>'image/jpeg',        // JFIF jpeg
  'FFD8FFE1'=>'image/jpeg',        // EXIF jpeg
  'FFD8FFE8'=>'image/jpeg',        // SPIFF jpeg
);
$signature = strtoupper(array_shift(unpack("H*", substr($imgData,0,60)))); // convert first 60 bytes of $imgData to a hex string

$imgMimeType = 'application/octet-stream';
foreach($magicNumbersToMimeTypes as $magicNumber => $mimeType) {
  if (StringUtil::beginsWith($signature, $magicNumber)) {
    $imgMimeType = $mimeType;
    break;
  }
}