Refactoring with use of separate to sub classes from Image. Add FileHelper to trying toString conversion. Add ImageCollection (not tested work).

FileHelper.class.php

@@ -0,0 +1,13 @@
+<?php
+
+class FileHelper
+{
+    public static function toString($object)
+    {
+        $data = array();
+        foreach ($object as $attribute_name => $attribute_value) {
+            $data[$attribute_name] = $attribute_value;
+        }
+        return json_encode($data);
+    }
+}