One thing I love to do is create ghost images. This is where we make it so that our subject is not entirely solid which gives the effect that they are a ghost. The technique behind these photograph is incredibly simple although reliant on meeting a few criteria:
You need a flash
You need some people who can take part in your photo
You need to take the photo somewhere there is some ambient light (this is crucial to ghosting)
You need something steady to hold the camera as we will be using long exposures (usually)
So something I should explain, a camera records light to make an image. It can only record what it can see. If it can't see you, it can't record you. If it can see you only then will it record you. If you have a shutter of 20 seconds, but if you're only visible for a tiny fraction of that time, say you're shooting in complete darkness and you fire a flash, then whatever was there during the flash duration is all the camera will see. This is the secret really to freezing action for things like high speed or for light painting. If there is ambient light, it will interfere with your photo because it will light you for the entire shutter duration so if you move, the camera can see you move and so you're more likely to blur. If there's something lit behind you and you move, the camera can see what's behind you and so blends you into the background. For ghosting, it is this principle we're trying to exploit.
29mm 5s F7.1 ISO 100 Flash Fired
Here, I had a five second duration. I ran out after the flash fired while my friend stayed put. This is why you can see through me but not her. The ambient light was provided by the street lamp. It's important that the camera can see something behind the ghost or it can't blend them. As you can see, my black jacket blended far more than my beige chinos. This is because darker objects are harder for the flash to imprint and so are more susceptible to blending.
So what's the basic concept here? Well we're going to be using slow sync flash. This is where we combine flash with a slow shutter speed. I usually use front curtain sync for my ghosting photos. All you need to do is set up your camera on a tripod and set a long-ish shutter speed. I find 5 seconds works pretty well for me. You then press the shutter button. What happens is that the person who is the ghost must run out of the photo after the flash has fired while the solid people have to remain as still as possible for the entire exposure. What you find is that the clothes that you wear and your skin tone will affect how well this technique works. Flash tends to imprint bright things much more easily than dark things. So if you're wearing black clothing, this will blend more than if you're wearing bright clothing.
35mm 4s F2.8 ISO 100 Flash Fired
Here the sky is behind her upper body so it blends better than her lower half which is in front of the ground which is poorly lit by comparison. It is also affected by her clothes.
I find shooting just after the sun has gone down to be best for ghosting. This is because it's dark enough for the flash to give a good imprint but also just the right amount of ambient light to give good blending. Remember though, for ghosting to work, you need ambient light or everyone will just appear solid as the camera has nothing to blend with.
You don't necessarily need a tripod to do this. I took the following photo hand held with a 1/2s shutter. I just asked my friend to walk across the frame while I was taking the shot.
18mm 1.6s F2 ISO 100 Flash Fired
18mm 2.5s F5.6 ISO 100 Flash Fired
So go and try it out and see what kind of effects you can get.