Q&A: How Does Digital Image Recovery Software Work?

Earlier in the week, I posted a collection of links for Digital Photo Rescue and Recovery Software. In the forum, Dave is asking "How Does it work?" Les provides a good answer.

In the wonderful world of computers, there is one important rule to remember: NOTHING IS EVER REALLY GONE! "Deleting" a file on Windows or Mac OS (Linux/Unix too) only removes a marker to the file. This makes it invisible to the casual user, and allows the OS to overwrite parts of the file if needed. The file is still there in all its glory, waiting for a recovery tool to find it. There are "milspec" wiping tools that allow you to do a pretty thorough job of obliterating a file, but they are not perfect by a long shot.

On flash memory cards, a similar truth holds. The usual problem which causes files to disappear is corruption of the directory. (This also happens on computer drives as well, esp. older file systems.) The directory is the "filing system" used by the card or computer drive. The simple analogy is to imagine that a malicious ex-employee at your company has mixed up all of the filing cabinets and removed the labels. The files are all still there; you just have to hire someone to manually leaf through the cabinets and find them.

This is not to say that all files can always be recovered. The files themselves may be corrupt; with a Word doc (for example), you can usually reconstruct it, but with an image, you may be SOL. Also, if the file has been heavily overwritten by other files, it will be useless. This is why if you accidentally delete a vital file, you should stop using that drive until you can recover the file.

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