Motivation
I have many images with multiple resolutions (therefore multiple aspect ratios),
I would like a function that cuts automatically these images to a fixed size.

Description
I don't know the initial aspect ratio of each images I can't calculate the every edges;
therefore the crop node will have to cut "automatically" to a "fixed" size
keeping each image centered (or other types of anchors)

generalizing:

• if the image are wider you will have to cut the left and right edges
• if the image are taller you will have to cut the upper and lower edges
• if the image is totally different you must cut all edges

on the contrary:

• if the canvas needs to be larger, borders must be added

Alternatives
paint.net has a similar function (canvas size), which is very useful,
let's call it an "advanced automatic crop" ;)