There is. The Android camera app has a button on the top-right corner that lets you quickly switch between saving to "photo storage" or "locked folder". If you pick "locked folder", it saves it to a special folder that isn't backed up to the cloud and requires a screen lock to open.
that does sound like a useful feature for uses like this, but I've never heard of it (and many phones probably come with different camera apps provided by the manufacturer... I have no idea if the Camera app on my Motorola phone is the stock one or not...).
