First way
This is only possible with a Digital SLR or a camera you can set the shutter speed and aperture (aperture = The amount of light that is exposed to the sensor).

You first need to on your camera is set the shutter speed as 10 seconds or more. Then set the aperture to a round f.15 so the photo isn’t overexposed. You will need to play around with the aperture until the image is correctly exposed. Remember a low number is a big aperture and a big number is a small aperture.

When you have the image exposed correctly with a long shutter speed, find an object that you want to be a ghost it can be anything even you! So get the object were you want it. Have the camera on a tripod or a stable surface. So then take the photo, leave the object in front of the camera for half the time of the shutter speed you set. You don’t have to do that but the longer you leave it the more solid it will look and more transparent if left for a short time.

Second way
If you have a version of Photoshop and you can’t set the aperture and shutter speed on your camera.

If you use auto mode on your camera to take a photo of an object then remove the object and take another photo. Keep the camera in exactly the same position or the effect will be spoilt.

After you have taken the two photos get them on to your computer and open Photoshop.

In Photoshop open both photos get the photo without the object in and create a new layer on top of that photo. Then go to the image with the object in it and copy it. You may have to select it first (PC ctrl a) (Mac cmd a). Then click edit in the menu bar and click copy. Then go back to the photo without the object in it. Then paste the image with the object in to the layer you created. Then you will see the image with the object in it. Then go to the opacity slider on the layers pallet and adjust the opacity until you are satisfied. Then save the image. Using Photoshop can enable you to have more control over the ghost effect.

You may not get the ghost effect right first time but if you persist you will get some very interesting results.