Take a photo.
Copy it to your computer.
Look at the Exif data using your favourite tool.
I use Gwenview to view the Exif data and on my D5100 photos I see three "values" named "Shutter count", "Shutter Count 1" and "Shutter Count 2". I don't know why there are three different counts, but only the first have a sensible value. Shutter Count 1 always shows 0. Shutter Count 2 shows a different, random value on every photo. I've long been wondering about that, actualy.