It isn't too well known that Photoshop can be used to create animated gifs. In this instructable, I will show you how to make a subject of your choice fade and disappear, then reappear in a gif, all from a single photo. With the basic photo example that I have used, it's not very Halloween-y, but some of your own time and skills, it wouldn't be hard to work in a few ghostly shivers or poofs of smoke!
You will need some knowledge of how to use Photoshop, but I haven't used anything really complex.

Step 1: For This 'ible

It is suggested that you have the following:

Internet connection
Photoshop (from CS3 onwards)
A photo to work on (should contain a subject which you want to disappear)
Patience

Got that? Alright, let's roll :D

p.s. I've put in the photo that I started with, if you wanted to use it as a practice. I just found it somewhere on the internet, and if it belongs to you, I apologise. No copyright infringement was intended.

Step 2: Pixlr-fy That Photo

To start off with, I wanted the image to have an old sort of feel. To obtain this feel, I went to Pixlr-O-Matic, uploaded the image, and chose the 'Julia' effect. You could choose any other effect, but I don't suggest that you add an overlay or a background, as it will make editing a little more finicky later.

Step 3: Photoshopping

Open the Pixlr-fied image up in Photoshop.
CTRL+J to duplicate the layer. Hide the background layer.
Select the subject that you wish to duplicate, in any way you wish. My subject was the boy in the back right.
Personally, I think that using the pen tool is the best, but you still get okay selections with the magnetic lasso.
Whilst your subject is selected with the marching ants, press CTRL+J again to create a layer from the selection.
CTRL+Click on the new layer; this will bring up the selection again.
Fill in the selection on the copy of the background image using the stamp tool.

Step 4: More Photoshopping

Once the subject on the copy layer has been covered up, deselect (CTRL+D) and go over the area with the spot tool (the bandaid). This ensures that the background seamlessly blends together.
Now, turn the subject layer back on again and check to see if everything aligns well. If not, you may have to do some fiddling.

1) If the subject layer is too small (i.e. when it is visible, there's a white outline all the way around it) you could copy it again.
CTRL+Click the subject layer to get the selection. Go to the Selection menu on the top of the screen, click Modify and then Expand. Expand by 2 pixels or so, and then press CTRL+J. Slightly blur the edges of this new selection.

2) If the background isn't very realistic, blur it all over. :P

3) If you'd like the background to become more realistic, you can draw in something in the space where the subject used to be. E.G. Using a natural brush, I drew the tips of a tree, basing the colours and design off another in the image.

Step 5: Animation

Open the animation window up (from under the Window menu, tick Animation).
On the first frame, make sure that both the copy layer and the subject layer are visible.
Duplicate the first frame, then hide the subject layer on the duplicated frame.
Select both frames, and tween them. To do this, press the button in the animation panel which consists of three overlapping circles.
Add as many frames as you'd like. I'd suggest 5-10, but feel free to add more if you'd like a smoother animation.
Press the play, watch and check the animation. Is it smooth enough?

Duplicate the first frame, and drag the duplicate to the end of the sequence.
Tween the second last and the last frames.
Watch.
Delay the frames as you wish. I went for 3 seconds on the first, middle and last frames, then 0.2 secs for the rest.

Step 6: Saving

When you are satisfied with your final animation, you can save it as either a gif or a video clip.
To save as a gif, go to File>Save for Web & Devices>Save.
To save as a video, go to File>Export, and then follow instructions.

I can see the potential for this in an innocent slideshow, or in a video with eerie accompanying music. This really isn't a very difficult project, so I'd love to see people try. Thanks for reading, and I hope you've enjoyed!