Imagecrop after upload from CP

Hi there

I want to create a fieldtype that lets my authors upload an image (like ft.file.php) that is checked whether its the right size or not. if not, i want to have my fieldtype show a crop-tool (like the one from the function edit_image). after uploading an image with ft.file.php there is this “edit image” lightbox…how do i include the crop-tool there?

best regards and just ask for further information. Jonas