All of those mentioned in the sidebar can be downloaded off the Web, and most have shareware or free trial download versions. Most of the programs operate in a similar manner. You are then prompted to add the file names in sequence that you wish to add to the animation. The program then combines the images and saves the resulting file in the proper format with the embedded instructions. The question about whether your image is a line drawing or photographic image is often a clue to the software whether to dither the image.
Many programs automatically dither vector art.
Dithering an image twice creates sprinklings of spare pixels in image areas that should be flat color. Occasionally, these can work in your favor, but they generally lower the quality of the finished result. Image b is a copy of Image a where the arm has been moved a few degrees to the right. The monitor image was also cropped out and resized and a finger of the right hand lifted to give the impression of typing. So with a static photographic image it is still relatively simple to give a feeling of movement.