http://www.nikonchat.com/nikon-camera-schools/

How to completely remove a photo on a Nikon camera?
Okay, so I'm borrowing a Nikon D40 from school. And I wanted to try how good it was, so I took a picture of my face .. When I put the camera USB on my computer simply click the 'delete' in the photo. He's gone now. But I want to make sure it is completely gone .. There is nothing wrong, but I do not want to cause problems!
Seriously just save the photos. Then go to the settings the camera and find the format settings and confirm to erase all data. Poof! Its always happened like magic. Then any format memory card inserted and then remove. Next format the internal memory built into the camera.
Nikon F2 Old School Sound MD2 & MB1