For those of you using iPhoto on the Mac — there’s an option in the newest versions of iPhoto that can have dangerous consequences.

Open up iPhoto, and under the iPhoto menu choose Preferences. Then choose Advanced. You’ll see a checkbox that says “Copy items to the iPhoto Library.” It looks like this:

This checkbox should always be checked unless you know what you’re doing.

If the box is checked, it means that when you add photos to the iPhoto library, it copies those photo files to the special iPhoto database. So all your photo files will be together on your computer.

But if the box is not checked, it means that when you add photos, iPhoto doesn’t copy those photo files into the database. Instead it just makes a link to the photo file that already exists. Which might be on a camera card, or in another folder, or on another hard drive. This will make it very hard to find a specific photo when you need it.

So go look in iPhoto right now and make sure that critical checkbox is checked.