Cropping images with RMagick after uploading with acts_as_at



I’m using acts_as_attachment to create thumbnails in a filesystem (no
problem there), but I’m having a rough time figuring out how modify
the image to crop it, and then put it back into the filesystem.

I think that I can pull the image OK and modify the Image OK with

So really I just need a pointer on putting it back into the filesystem
as a modified thumbnail, but a semi-complete example would be a bonus.