Your camera's "Delete photo" setting doesn't really let you delete photos. It tells the card to hide them instead. Bad idea.
Al Fasoldt's reviews and commentaries, continuously available online since 1983


An innocent mistake can ruin your memory card

By Al Fasoldt
Copyright © 2011, Al Fasoldt
Copyright © 2011, The Post-Standard

Digital cameras store their photos on memory cards. These cards seem reliable enough, but an innocent mistake can wreck a card and ruin all the photos on it.

What's more, I'd guess most casual photographers don't even know this mistake exists. In all the classes I've taught on digital photography, I've found only three or four people who knew the essential technique that virtually guarantees this mistake can't happen.

The problem? I'll explain it shortly. Let me tell you the basics first, so you'll have something to go by.

Most cameras let you delete any photo after it's taken. This is handy when you do what I sometimes do -- take a picture of the floor -- or when you snap a photo that's too blurry to make out.

You don't have to be a photo genius to extend this idea one step further. If you can delete one photo, why not two? Or four? Or all the photos on the memory card once they've been transferred to your computer?

That seems to make sense. First you get your pictures onto your computer. Once they're safely on the computer, you need to free up space on the memory card for more photos, so you delete the ones that are on it.

Sounds like a good habit.

Sounds like an innocent habit, too. Yet it's one of the worst things you could possibly do.

You see, your camera's "Delete photo" setting doesn't really let you delete photos. It tells the card to hide them instead.

The world is full of little "gotchas" like this. Two by fours aren't two by four, and we have a habit of parking in a driveway and driving on a parkway. And, alas, your memory card doesn't really delete photos you tell it to delete.

Memory cards work like a drunken file clerk who has been told to toss out last year's annual report but instead simply takes the "Annual Report" label off the filing cabinet. The tipsy method is faster than actually taking the entire file out and giving it the heave-ho.

And that's why your camera doesn't bother with all the trouble of tossing out pictures you want to delete. That would take too much time. It just tells the memory card to cross off the label. No label, no file. That's how the camera looks at things.

But that's bad news for you. The stuff that was supposed to be deleted is still there, taking up space. When the office staff (or your camera) wants to have something new filed away, the new files have to go where the old stuff -- the old, hidden and not really deleted stuff -- is stored.

Uh-oh. Even Newton knew that two things couldn't be in the same space at the same time. So the camera tells the memory card to stuff that new photo in the old space. Remember now, that's old space isn't really space; it's like a closet that's already full. Stuff inside has to go bye-bye.

Doing this a dozen times -- or maybe a hundred times -- on your memory card makes a mess of the card's formerly neat way of labeling and storing things. The labeling part of the operation, using what's called the "table of contents" -- yes, just like your old schoolbook -- suffers the most.

I'm not exaggerating when I say the card's table of contents is guaranteed to get confused. And when that happens, your photos aren't where they're supposed to be on the card. Your camera can't find them and your computer can't find them. You lose them.

What's the solution? It's called "formatting." This wipes the card clean, digitally speaking. It erases all those confused entries in the table of contents and gets the card ready for a fresh set of new pictures.

Look in the camera's menus for an option called "format" and be sure to format the card after every use. A freshly formatted memory card is very unlikely to lose your pictures.