on github or on www.thomas-lauria.de you will find a Image Crop Utility written with Ext JS.
The Utility calculates only the crop coordinates and measures. This data can be send to the server, where you have to implement the image crop itself.
For example in PHP:
I hope someone will consider this cropper for usefulPHP Code:
$t = new Imagick($imagepath);
$t->cropImage($crop['width'], $crop['height'], $crop['x'], $crop['y']);