You will need some knowledge of how to use Photoshop, but I haven't used anything really complex.
Step 1: For This 'ible
Photoshop (from CS3 onwards)
A photo to work on (should contain a subject which you want to disappear)
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
Step 3: Photoshopping
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
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
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.
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
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!