the present invention is directed to a system and method for providing single instance storage of previously backed up data objects in archived backup storage , also known as data deduplication . current deduplication methods implemented during backup and archiving of data do not work with previously backed up data . previously backed up images may vary in format depending upon the method of backup and the type of backup system used . as a result , while future backup efforts may prevent multiple instances of backup data , previously backed up data may exist in multiple instances , wasting valuable storage space . the present invention decodes previously stored backup images for deduplication using an image adapter module that works cohesively with a deduplication engine , regardless of the format of the previously backed up images .