A disk image is a single file containing the complete contents and structure representing a data storage medium or device, such as a hard drive, CD, or DVD. A disk image file is usually created by creating a sector-by-sector copy of the source media, ignoring its file system, and thereby perfectly replicating the structure and contents of a storage device.

Some disk imaging utilities omit unused file space from the source media, or compress the disk they represent to reduce storage requirements, though these are typically referred to as an archive file, as they are not a literal disk image.