some dslrs can do it in camera. otherwise you take 3 shots in quick succession, open them as separate layers in photoshop then merge the layers together.
You can try this. 1. Background totally black if possible. 2. Set to bulb or 5-10 second shuttle speed. 3. Use tripod, if possible. 4. After composing, with luck, click the shuttle 5. Close and open the lens (where the light passing through the lens) using the black cardboard to control the number of multiple images to capture. 6. If you open and close the lid too fast let say in 4 seconds, you can just close the lid and let the shuttle finish the remaining time.