Check if file exists, and if it does roll a new filename.

classes/upload.class.php

     }
 
     public static function handleUpload($file = false) {
+        $cwd = getcwd(); // Our websites CWD (Current working dir)
         $filename = $file['name']; // Get filename
         $size = $file['size']; // Gets filesize
         $tempname = $file['tmp_name']; // Where did php upload our data to?
         $ext = explode('.', $file['name']); // end() doesnt like us using explode directly.
         $extension = strtolower(end($ext)); // Get the extension of the file.
         $randomname = Upload::generateRandomString(); // We give our file a random name - It will be this.
-
-        $cwd = getcwd(); // Our websites CWD (Current working dir)
+        
+        // If filename exists, we roll a new one.
+        while (IS_FILE($cwd .'/'. Config::$file_path . $randomname . '.' . $extension)) {
+            $randomname = Upload::generateRandomString();
+        }
+        
+        // We got our unique filename, lets continue.
+        
         $uploadPath = $cwd .'/'. Config::$file_path . $randomname . '.' . $extension;
 
         if (!in_array($extension, Config::$file_types)) {