Hi, @cpagit the easiest way would be to first upload the image (from a file input), in a second step display the uploaded image with Guillotine to allow the user to set what she wants and finally crop the image server-side using the data you get from Guillotine.
Beyond that... it depends on your particular case, your server and the software you'd use to process the images. Explain a bit more about what you have and what you're trying to do, maybe I can point you in the right direction.
Thanks Matias. I'm actually trying to resize the original image with JAI. I thought initially that guillotine was able to send me the transformed image but I understand now the guillotine only sends me the x, y , scale and angle. It would have been nice... In a future version may be?