Cnw Recovery will work with either a physical hard drive, or with a DD image file.  To select the image file, use the drop down drive select box at the top of the screen and select 1: Image file and Backup files.

The screen below will be displayed

The browse function allows an image file to be selected.  This can either be a DD type image, or a supported backup file, such as a Microsoft MTF file

The drive type actually selects the block size.  For a hard disk, the block size is 512 bytes (or 0x200).  A CD and DVD have 2048 byte blocks.  Optical disks come in several variations, which may be selected.

The Image file is in sections (not yet implemented) will allow for systems that generate files, typically in DVD size sections

Shadow Drive

The shadow drive is a useful feature when a disk has only been partially imaged.  This may be the case for a disk with many failures.  If this option is enabled, a physical drive can be set as a shadow drive.  When the disk image is read, and the sector is determined as unread, or failed, the program will try and read the shadow drive.  If successful, the disk image will be updated,  If unsuccessful, due to a total sector failure, the disk image will be marked to indicate that the sector can not be read.  This process ensures that the drive is not worn out by many sector retries.