resample image

CKFinder resizes uploaded images automatically if they exceed the maximum size:

$config['Images'] = Array(
      'maxWidth' => 1600,
      'maxHeight' => 1200,
      'quality' => 80);      

(you can change the maxWidth/maxHeight settings in config.php).

If you need to resize only specific images during upload, take a look at the following thread:
viewtopic.php?f=10&t=10846&p=28608&hilit=resize#p28608