Interesting recommendations - thanks. Ultimately, I want to use Automator so that I can drop an image into a folder, this then copies that image, changes the size, sets up the crop rectangle. Next, I manually adjust the rectangle height so I crop off a bit of the top or bottom. Then, have another Automator action that saves the file after optimising it or converting it to jpg.
Or...maybe even have the whole process automated and instead of manually cropping the top or bottom off the image, have automated produce two versions to cover both crops. That would be lovely.