image rotation in twitter card

src/app/views/base.twig

@@ -15,7 +15,7 @@
       <meta name="twitter:site" content="@Level2Lu">
       <meta name="twitter:title" content="Level2 | a hackerspace in Luxembourg City">
       <meta name="twitter:description" content="Check out whether we're open, how many people are present right now or what events are scheduled to happen at our place. Swing by to say hello and become a member if you like to =]">
-      <meta name="twitter:image" content="https://files.level2.lu/photos/twitterCard.jpg">
+      <meta name="twitter:image" content="https://files.level2.lu/photos/twitterCard.php">
     {% endblock twitterCard %}
 
     <title>Level2{% block title %}{% endblock title %}</title>

twitterCard.php

@@ -0,0 +1,34 @@
+<?PHP
+# stackexchange2php("https://stackoverflow.com/questions/15151051/url-to-a-random-image")
+function random_pic($dir = 'imagerotation') {
+    $files = glob($dir . '/*.jpg');
+    if (!$files) return false;
+
+    $file = array_rand($files);
+    return $files[$file];
+}
+function outputImage( $filename ) {
+    header('Content-Description: File Transfer');
+    header("Content-type: image/jpeg");
+#    header('Content-Disposition: attachment; filename='.basename($filename ));
+    header('Content-Transfer-Encoding: binary');
+    header('Expires: 0');
+    header('Cache-Control: must-revalidate');
+    header('Pragma: public');
+    header('Content-Length: ' . filesize($filename ));
+    ob_clean();
+    flush();
+    readfile($filename );
+    exit;
+}
+// Get a filename
+$filename=random_pic();
+// Check that a file was found
+if (!$filename) {
+    header('HTTP/1.0 404 Not Found');
+    die();
+}
+
+// Output the image
+outputImage( $filename );
+?>