elFinder

Here is example of rename callback.

--- elFinder.class.php.orig    2010-03-22 05:05:08.000000000 +0300
+++ elFinder.class.php    2011-02-11 01:10:07.000000000 +0300
@@ -596,9 +618,11 @@
                 } elseif (!$this->_isUploadAllow($_FILES['upload']['name'][$i], $_FILES['upload']['tmp_name'][$i])) {
                     $this->_errorData($_FILES['upload']['name'][$i], 'Not allowed file type');                    
                 } else {
-                    $file = $dir.DIRECTORY_SEPARATOR.$_FILES['upload']['name'][$i];
+          $fname = $_FILES['upload']['name'][$i];
+          $this->_fnamereplace($fname);
+                    $file = $dir.DIRECTORY_SEPARATOR.$fname;
                     if (!@move_uploaded_file($_FILES['upload']['tmp_name'][$i], $file)) {
-                        $this->_errorData($_FILES['upload']['name'][$i], 'Unable to save uploaded file');    
+                        $this->_errorData($fname, 'Unable to save uploaded file');    
                     } else {
                         @chmod($file, $this->_options['fileMode']);
                         $this->_result['select'][] = $this->_hash($file);
@@ -1855,6 +1879,10 @@
         return (double)$time[1] + (double)$time[0];
     }    

+  public function _fnamereplace(&$filename) {
+    
+  }
+  
 }

Using callback:

  class elFinderDrupal extends elFinder {
    public function _fnamereplace(&$filename)  {
      $filename = preg_replace('/atv/','bike--', $filename);
    }
  };

So atv1.jpg will be renamed to bike--1.jpg.

Note: only filename passing to callback, so better pass full path to allow moving to another directory, log to database, etc.