Typically when "cloning" you are simply hooking up a new drive to a SATA port on the computer or you are using a SATA to USB 3.0 adapter with the new drive attached to it and you are copying the old drive straight over to the new drive. It's usually a fast process and after it's done you remove the old drive and install the new drive.
A "backup image" is when you might be hooking up a USB 3.0 External Hard Drive and running a "Backup" from the existing drive to the attached external media. After it is done you have a "backup" of that original hard drive on external media. You then install the new drive (SSD) into the computer and run your imaging software at boot to restore the "Backup image" you just created from the External Drive and restore it to the new drive. This of course takes longer than a clone because it's a two step process of backup and restore.
A "backup image" is when you might be hooking up a USB 3.0 External Hard Drive and running a "Backup" from the existing drive to the attached external media. After it is done you have a "backup" of that original hard drive on external media. You then install the new drive (SSD) into the computer and run your imaging software at boot to restore the "Backup image" you just created from the External Drive and restore it to the new drive. This of course takes longer than a clone because it's a two step process of backup and restore.