This is a very simple tutorial on some ghostly photo editing techniques using Pixlr. While the basic principles can easily be applied to any photo editing software, I recently discovered Pixlr and as it is free, online and equipped with most of the tools a retail editor like photoshop has, I felt it was more appropriate to give the instructable from the point of view of a Pixlr user.
Step 1: Tools
A short list I know:
Step 2: Taking The Photos
This can actually be one of the more difficult steps. The idea is to take two almost identical pictures. Background movement in particular should be kept to a minimum. Set up your tripod or other very stable substitute and take a couple of pictures without anything in the scene. Once you're happy with the set up and have a few empty photos you can put your subject (I just used myself) in the scene. Standing on something like a milk crate will let you add a floating effect to your ghost.
My advice with this step is take lots and lots of photos. The more you have then the more you can choose from and it's better to have it and not need it than... well, you know! You'll probably be a small bit concerned about posing for the photo, don't worry about looking stupid, nobody's going to see anything but the finished product..... unless you decide to post an instructable about it.
Step 3: Setup
Go to Pixlr.com and open the advanced editor. Open two images; one without the subject (from now on called image (a) ) and one with the subject (image (b) ). Select image (b) and double click on the padlock icon in the Layers palette to unlock the image, you can then drag image (b) directly over image (a). Try to line up the images to overlap as much as possible.