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forensic image

What is a forensic image?

A forensic image (forensic copy) is a bit-by-bit, sector-by-sector direct copy of a physical storage device, including all files, folders and unallocated, free and slack space. Forensic images include all the files visible to the operating system (OS), as well as deleted files and pieces of files left in the slack and free space.

Forensic imaging is one element of computer forensics, which is the application of computer investigation and analysis techniques forensic examiners use to gather digital evidence for presentation in a court of law.

Not all imaging and backup software creates forensic images. For example, Windows backup creates image backups that aren't complete copies of the physical device. Forensic images can be created through specialized forensic tools, such as forensic software. Some disk imaging utilities not marketed for forensic use also make complete disk images.

Forensic imaging in cybersecurity

In the case of cybercrime, additional evidence might be discovered other than what is available through an OS. This type of original evidence includes incriminating data that has been deleted to prevent electronic discovery. Unless the data is deleted securely and overwritten, it is often recoverable with forensic or data recovery software.

Creating forensic images and backing them up prevents data loss from drive failures. The loss of data as evidence can be detrimental to legal cases. Forensic digital image files can also prevent the loss of critical files in general.

The three types of forensic images

When capturing the contents of a storage device, three types of forensic images can be created. Which approach is used depends on the technology available and business requirements. The three types of images include the following:

  • Physical image. This image captures the entire contents of a storage device, including active data, unused or unallocated space, and deleted data that might still reside on the storage unit.
  • Logical image. A storage device is scanned to obtain this data, which is, in most cases, active data.
  • Targeted image. Specific data, such as that required for a legal examination, is identified and imaged.

Capturing and creating a forensic image

Generating a digital forensic image of a storage device requires tools and software to scan the device, capture the desired content and provide an exact copy of it to another storage device. Almost any device that has a storage function or capability can create a forensic image. For example, hard drives, CD-ROMs, flash drives, mobile phones, computers, smartphones and even web pages can all do this.

As an example, OpenText EnCase Forensic is software that creates an image format for storage and future forensic analysis. A successful forensic image has the following characteristics:

  • The device being scanned and the scanning technology are successfully connected.
  • The source device and its data haven't been modified.
  • The scanning technology generates a true copy of the data to be scanned.

Write blocking is a technology that prevents any changes to the source device before and during the scanning process. Write blockers typically sit between the source and the scanning system and are available for different storage devices.

Diagram of forensic imaging process
When data is scanned as part of a forensic imaging process, a write blocker is put in place so the data and the drive it's on can't be altered. The data is then scanned and formatted for storage and analysis.

Why is forensic imaging important?

Forensic imaging prevents the loss of original data. These imaging tools and techniques are the only way to ensure that electronic data can be successfully admitted as evidence in a court or legal proceeding.

A detailed image of a memory system or primary storage device provides accurate information on the contents of the device, enabling forensic experts to diagnose existing and potential problems. However, for a legal or compliance audit as part of a forensic investigation, law enforcement needs accurate and verifiable data.

Learn more about the tools and techniques required in a cloud computing forensics investigation.

This was last updated in March 2023

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