I've just never imaged because I didn't understand it. I do understand that clone is an identical copy, imaging, I don't know what or how it works.
Cloning is a real time transfer from one hard drive to another. The receiving hard drive should boot if all went well. Think of it as a single operation. It's isn't a backup in the normal sense of the word and is typically used when all is well and you want to move from one working system to another.
Imaging has two operations: 1: you make an image file of a partition and store it on some other partition. It's just a file like any other file and isn't bootable. 2: at some future point, you "restore" that image file to a partition. It's the restoration process that makes the receiving partition bootable and usable. When you want to restore, you must boot from disk or USB drive that you prepared previously. If you can't boot from this disk or USB drive, you can't restore.
It's a backup as normally understood. You can make and keep an image file for every day of the week if you want and later restore whichever of those you want. You might restore an image after a hard drive failure, after a major virus attack or unknown corruption, or after buying a new hard drive.
They have some similarities, but imaging is more flexible and less prone to failure.