Image cropping on upload

II'm trying to have my images do the following after upload:

1. If greater then 2000px wide then resize down to 2000px (I got that functioning ok as of now)
2. crop off the top and bottom 25% of the image to make it rectangular.

MY my problem lies in trying to figure out how to crop that 25% off the top and bottom equally no matter what the height is.. I can't control all the possible different sizes a user might upload (height and width) I just know I need it about 2000px wide and the height be around 650px (roughly) and cropped at the top and bottom.

Could anyone help help me with writing something like that up?

Thanks allot