Photo File Validation

I know I’ve been dragging my feet on posting my photos here, and I have a ton of catching up to do. But I really need to write about ImageVerifier, a program I discovered via the Digital Photography Best Practices and Workflow site, which is one of the most important applications every photographer should have in order to be sure their image files still work. I know that sounds a little over the top, but I feel very strongly about this. I’ll describe the problem, then the reason for this solution.

Your hard drive is the new shoebox-in-the-closet or drawer-in-the-basement full of photos. With that drawer full of photos, you knew that if you kept them out of floods or fires, the pictures were probably ok.

With a hard drive sitting on a shelf, you don’t know if the pictures in it are ok. We joke about bit rot being a real thing even though it doesn’t work that way. But, the effect is real. Files and drives go bad from time to time, due to mishandling of drives, system crashes while editing images, or just Murphy’s Law. The bearings in that drive sitting on the shelf with your backup might be getting just dry enough that if you don’t plug it in this week, it won’t spin up next month when you need it. When you get the click of death you know the drive is toast. But even when the drive mounts fine, there may still be silent errors you don’t know about.

So, here’s the problem. You have thousands and thousands of photos starting years ago on your hard drive, and you copied them to a second hard drive, so you feel safe knowing your pictures are backed up.

But one day when you’re looking for an old vacation photo and it doesn’t open, you plug in that backup drive, and the file is bad there too. You needed a way to make sure all your images were valid before backing them up. You could open each image in your photo viewer, but that would take forever and you’re certainly not going to do that on a regular basis. You might even have stacks of hard drives (or CDs) on a shelf, which makes the problem even more daunting.

This is a problem that I’ve been thinking about for years. While photography is my hobby, my dad is a professional and I help him out with his technology. He has those stacks of drives and discs I mentioned above. I searched high and low for a program that would make sure files haven’t become corrupt over time, but couldn’t find one. I even wrote some shell scripts to store checksums and then compare them later. This might work for my own use, but it wasn’t something I could have other people use.

Then I stumbled across ImageVerifier, which will do exactly what its name says. This $40 program for Mac and Windows is used in three steps: verify images, save hashes, compare hashes.

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First, you verify your files. This step actually looks inside each file and confirms that it is an image file. For example, JPEGs are probed for details that would reveal file corruption. RAW files are opened with the Adobe DNG convertor (a required helper program) to peek at the image data. DNG files have a data checksum in the file when it was created, and these checksums are verified. Other image types are also handled.

This step reports any errors that are found, so you can do something about it (restore a corrupt file from a backup; delete a file deemed safe to delete; etc.)

The second step, storing hashes, is performed after all images are verified. These hashes are checksums of files saved to a database used by ImageVerifier. This step must only be performed on valid files, because the hashes will be used in the next step at a later time.

The last step is to compare hashes. Once hashes are created and stored, you never have to do a full image verification again.

The reason for all this hash business is that comparing hashes is much faster than doing a full image verify. Naturally, if you have all the time in the world, you can skip the hashes and always do a full image verification.

So, every six months or so, you run a compare hashes operation on your drive or disc, and you’ll know that those files haven’t become corrupt and haven’t been altered in any way. The Mac version can even run a verification on a schedule. I set mine to verify hashes on the first day of the month, at least for files on my computer. Cold or offsite storage will obviously have to be run manually.

As a result of using this application, you can rest at night knowing that the multiple copies of your photos are actually usable.

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