Image Uploading and Editing Tool

I need an image upload / resize / crop tool added to a php site. The user will be able to go into the back end of the system (already built)... edit an item in the system and click upload image. After the image is uploaded, the user should be able to crop the image to a square. When they click Save... the system will create a normal sized image of a predefined size - example 250 x 250 pixels, and a thumbnail size of say 80 x 80 pixels.