Rescuing Lost or Damaged Digital Images
Back when I was shooting film, I can remember being down at Mt. Rainier one beautiful summer morning when something unexpected happened. Finishing a roll, I rewound the film so I could put in a new roll. The camera made the usual whirring sound and when it finished, I opened the back of the camera. To my shock, the film had in fact not rewound, and it proceeded to spring out from the take-up reel all over the place. Needless to say, all the images were ruined. You might not think that digital images could suffer a similar fate but they can. Here are two indispensable tools that can save them.
First, a few basics of how memory cards store digital images. The file system on your card is the same one used on many computers. A "File Allocation Table" or FAT serves as a table of contents to let your computer know where each file lives on the card and how big it is. The file name, creation and modification dates and other information lives in the FAT too — everything other than the actual contents of the file. The data that makes up the file itself have documented formats also. This is how programs like Photoshop and other image editors are able to read and understand them. The file may in fact be fragmented into a number of linked extents scattered around the card, as space permits. The parts are automatically reassembled in the correct order when you open the file.
When you delete a file, its entry in the FAT gets removed, but the file contents itself doesn't. That space becomes available to be overwritten simply because nothing in the file allocation table says its in use. When you then create a new file, the data gets written in a free area on the card and an entry for it is made in the FAT. Until overwritten though, the bits and bytes that represent the deleted file are still there if you know what to look for. If you do, you can create a new FAT entry for it to make it accessible again. And if the file has become corrupted but you know enough about how it is supposed to be structured you can sometimes rebuild the missing bits to give you a usable image again.
The two programs we'll discuss here are experts in this sort of forensic analysis and reconstruction. Both programs can recover files of any type, but they specialize in image files. Both are available for Windows and Mac OS X.
Lexar makes some of the best compact flash cards you can get. Their professional line of cards includes a copy of a program called Image Rescue on the card. If you buy a Lexar Professional card, don't just format it and go out shooting. You'll want to copy the Image Rescue program to your computer first. You may not need it or even care what it's for now, but you could some day.
Image Rescue is a specialized data recovery program that understands the format of jpeg, tiff and a number of common types of raw files. If your card becomes corrupted or you accidentally delete some images from it, Image Rescue may be able to save them. The recovery function can operate in any of three modes.
A High Level Search is the quickest recovery method and can recover your images if they were deleted but otherwise intact. A Low Level Search scans the card looking for data that is structured as an image in one of the supported formats would be. It then puts the fragments back together to form files again. Since the file system FAT information though was gone, Image Rescue must come up with new names for recovered files. Jpeg files will be named with a .jpg file extension, but all tiff and raw formats recovered will be given the .tif file extension due to the similarity between tiff files and many raw formats. You'll need to review the results and rename them to match the actual format based on what camera you were using. Lastly, the Extensive Search option goes one step further and tries to create image files even if the program can't find all the pieces of the original. As such, it will likely create numerous fragments of images that you'll end up just deleting, but it may be able to salvage some images the other Search modes can't. Recovered images are safely written to a folder of your choosing on your hard drive so you won't overwrite your original damaged files should you need to resort to other methods of recovering them.
For convenience, Image Rescue also includes functions to test your memory cards, format them, securely erase them, and display information about them. You can also update the firmware on USB enabled Lexar cards.
If you use other brands of memory cards, you can still buy Image Rescue directly from Lexar for only $29. The original release of Image Rescue only worked on Lexar cards, but current versions support all makes and kinds of memory cards.
Another option is PhotoRescue from DataRescue. You can run PhotoRescue either in a simplified Wizard mode or in Expert mode. The Wizard mode will default to standard settings and start doing its thing. The advanced Expert mode allows you to specify drive parameters allows the choice of either fast or slow recovery methods. Expert also lets you do partial media recoveries and features advanced jpeg reconstruction methods. Both modes offer "12 advanced recovery methods" according to DataRescue. Both modes provide thumbnail views of found images so you can select which ones you want to restore. Unlike Image Rescue, PhotoRescue seems to be able to get the file extension correct on camera raw files so you won't need to rename your .NEF files from the default .tif extension.
Especially in Expert mode, the program will ask you about technical parameters of how your card is formatted, but in my experience it intelligently defaults to the right choices all on its own so you don't need to be an expert yourself to use Expert mode. If your memory card is so corrupted that your computer doesn't even know to assign it a drive letter, PhotoRescue can still attempt to recover images from it by reading the physical drive itself rather than the logical drive letter. Neat trick.
You can download the demo from the company's website and if it can see your lost images, you can buy the program for $29 and DataRescue will guarantee the files will be recovered or your money back. The price will soon go up to $39 according to their website. The demo version will recover non-image files for free. Updates are free for one year from the date of your purchase so set yourself a reminder to download the latest before your year is out.
PhotoRescue claims to have independent tests showing they can recover more than their competion, but both it and Lexar Image Rescue are highly recommended. PhotoRescue concentrates exclusively on recovery features and may have a slight edge on Image Rescue, while Image Rescue distinguishes itself with its format, erase and other add on features.
I've been reasonably lucky. I only ever had that one roll of film fail to rewind. The end of the film had come loose from the spindle inside the film canister so even though the camera thought it was rewinding it, it really wasn't. I've (so far) only had problems with lost digital images once so far too. But unlike those film shots from Mt. Rainier, the digital images weren't gone forever. I had my copy of PhotoRescue with me on my laptop and it saved the day. I got my images back, safe and sound.
One thing to keep in mind with both of these programs is that if you find yourself with card problems is to not use that card any more until you recover your lost images from it. Once they have been overwritten with new files, they are gone for good.
PhotoRescue version 3
There are no easy answers if your film fails to rewind, but if you are shooting digital, a bit of preparation now can go a long way toward saving your images if they ever get lost or damaged in the future. Rather than waiting to encounter this problem yourself, my recommendation would be to get either Lexar Image Rescue and or PhotoRescue from DataRescue now. Heck, they're cheap enough that you might want to consider having both for extra insurance. That's what I did.
Update 3/20/2007 - DataRescue has just released version 3.0 or PhotoRescue featuring a new wizard interface and even better recovery algorithms. OS X users will appreciate the native Intel Mac support. You can also now get a dual platform license. A nice upgrade, and not expensive at all.