What's the difference between a drive image and a drive backup?

I can restore a computer with an image if it's the image was made from the same computer. With a backup I can use it on any computer. So what is it that makes these two methods different?

An image is basically a bit by bit copy of your hard drive. This is why you can only restore it to the same computer (or one with identical hardware).

A backup is data and settings that tend to be OS independent. It is like making a copy of a folder, that folder and its contents will work on any computer that can read the files in the folder. This is why your backups are important in case of file corruption. You don't need to reinstall the OS, just restore the file or files that were corrupt.

Clear as mud?

To add onto the first post, an image is one big file that cannot be changed. It has to be put back on and then you can change the files.

A back up is generally just a second copy of files. This means you can change them, move them and do whatever you want to them

Image = "photo" of the info. on the drive. You cannot run the programs in this form.

Backup = a duplicate of the drive. Programs are runnable from this.