Image-based backup is the practice of backing up an entire storage media by creating an "image" of the disk or drive. This backup solution, which is popular in many enterprise systems, involves cloning the whole storage media or an operating system partition instead of backing up individual files.
Techopedia explains Image-Based Backup
Image-based backup is an alternative to file-based backup solutions. At a glance, the former may seem much less efficient or redundant because of the need to back up all sorts of items that might not be needed when a system goes back online. In some ways, however, image-based backup is much more efficient. Experts explain this as a "time value" problem: one of the biggest reasons why businesses may choose image-based backup is that, after an emergency, the system can go right back online because all of the involved data, up to the operating system level, have been securely backed up as a whole unit. With file-based solutions, IT managers may need to reconstruct other parts of the system in order to get normal operations running again — and that can take time, time that is valuable to a company.
The practicality of an image-based backup depends on available storage resources. If the company can afford to use much larger backups and keep all that data on hand, even temporarily, then image-based backup can make sense. However, if much larger backups cause too much bloat or consume too many system resources, it may not be feasible.