I have recently just made a small app / class to crop images using this excellent js image cropping tool,  found here: http://www.defusion.org.uk

I have stripped out all the shit, default config is to maintain a specific aspect ratio and with a minimum size, however this can be changed by looking @ the defusion examples

Click here to download the js cropper with the php GD 2 crop functionality.

**Note: Have to set file permissions on the /cropper folder so it can write the image once its been edited.