Old bit of code that used Face.com API to auto crop images with just php.

Facial Auto crop

<?php

// Face.com api licence 
$FaceAPI_Key = '[enter your key]';
$FaceAPI_Secret = '[enter your secret]';

// Get image url
$imgSRC = urlencode($_GET['url']);

// cURL ALT method
$url = 'https://api.face.com/faces/detect.json';

// Image Parameters
$params = array('api_key' => $FaceAPI_Key, 
            'api_secret' => $FaceAPI_Secret, 
            'urls' => $imgSRC,
            'detector' => 'Aggressive',
            'attributes' => 'all');

$result = geturl($url, $params);

// Decode to an object
$imageData = json_decode($result);

// Results are in pixles
$width = $imageData->photos[0]->width; // full image width
$height = $imageData->photos[0]->height; // Full image height

// These are results 
$X_face = 10 + $imageData->photos[0]->tags[0]->width; // Face Width % of full image. Add 10% for padding
$Y_face = 20 + $imageData->photos[0]->tags[0]->height; // Face Height % of full image. Add 20% for padding

$X_face = ceil($X_face / 100 * $width); // Convert Face width from % to pixels
$Y_face = ceil($Y_face / 100 * $height); // Convert Height width from % to pixels

$X_pos = $imageData->photos[0]->tags[0]->center->x; // face center X %
$Y_pos = $imageData->photos[0]->tags[0]->center->y; // face center Y %

$X_pos = ceil(($X_pos / 100 * $width)-($X_face/2)); // Convert Face X position from % to pixels
$Y_pos = ceil(($Y_pos / 100 * $height)-($Y_face/2)); // Convert Face Y position from % to pixels

// cURL Function
function geturl($url, $params) {
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($params, null, '&'));
    $ret = curl_exec($ch);
    curl_close($ch);
    return $ret;
}


// Create image instances
   $src = imagecreatefromjpeg(urldecode($imgSRC));
   $dest = imagecreatetruecolor($X_face, $Y_face);

// Copy
   imagecopy($dest, $src, 0, 0, $X_pos, $Y_pos, $X_face, $Y_face);

// Output and free from memory
   header('Content-Type: image/jpeg');
   imagegif($dest);

// Do what you want with $dest (eg: copy to cache)

// freeup memory
   imagedestroy($dest);
   imagedestroy($src);
?>