Step 1: Take Pictures
As I'll show later on, having a steady hand is marginally important; just try to get the same general area in every shot. My technique in this particular case was to point the camera in such a way that the viewscreen showed the exact same object in the corner -- a small garden decoration -- in each shot.
Take as many as you like, until your arm gets tired, or until your camera runs out of memory! For this example, eleven shots will suffice. Make sure the shots are evenly timed, as good as you can. The more evenly-spaced they are, the smoother your animation will look in the end. For fast clouds, like here, I spaced the shots 2-3 seconds apart. For slow clouds, 5-10 seconds is better.
Step 2: Put the Pictures on Your Computer
In my case, my pictures were located on a memory card in my cell phone, which is what I used to take the pictures. I put the memory card in an adapter and plugged it into my laptop as a flash drive. Other devices will probably be more cooperative for you; most digital cameras utilize a simple cable to connect, or even transfer files wirelessly.
Save the pertinent pictures in their own folder. Make sure to keep them in the order in which they were captured. Some cameras have ridiculous naming conventions for the files they create, so this may be difficult. Windows does a pretty good job of sorting them properly if you select the "modified" option under "arrange icons by..."
Step 3: Open GIMP and Find a Landmark
If you don't already have GIMP, I highly recommend downloading it. It's a powerful bit of image-editing software, and it's free!
Look at the photos you took. Notice how, despite your best attempts, the pictures have a bit of a "wobble" due to the manner in which you took them. In my case, I was merely standing with my cell phone camera taking a bunch of shots. I didn't use a tripod or anything to stabilize my hand as I pressed the shutter release.
Try to find a picture that generally averages the positioning of the others. All the others seem to have captured landscape a bit to the left or the right of this one, or higher up or down. Open GIMP and drag this "average" photo into the blank window.
Find a place in the photo that is common among all the other pictures, like a bit of landscape that never moves. You want it to be small as well as easy to notice. The closer to the center of the picture this landmark is, the better. Hover your cursor over a specific pixel on that landmark and notice that GIMP tells you in the bottom-left corner the coordinates of that pixel. You may want to write it down.
A fellow Instructabler has notified me that there's a program you can use that makes this process easier, Hugin. It comes highly recommended!
Step 4: Begin Layering
Select the "Move" tool in the toolbox. Now drag photos onto GIMP one by one as layers, in the order in which you captured them.
Each time you drag a layer onto GIMP, use your "move" tool to click on the pixel in the landmark you identified, and drag it over to the exact coordinate location you wrote down. If your pictures are rather large, you may want to zoom in to more easily distinguish pixels from each other.
Step 5: Other Processes
For my own purposes, I only really needed to scale it down. Select in the menu "Image > Scale Image..." A good setting for this would be 800x600 or less. If the picture is too big, your computer will be slow while trying to load it up later.
To better optimize file size, you can select in the menu "Filters > Animation > Optimize (For GIF)" and it will reprocess each layer for conversion to a GIF file. This will open up in a new window. To make sure your animation looks correct, select in the menu "Filters > Animation > Playback..." This will open a preview window to show roughly how your animation will look.
Step 6: Save As GIF and Show Off
Depending on how many layers/frames you included in your animation, the rendering may take a while. When it's finished, open it for a test to see how you like it!
Share your time-lapse photography project with your friends and family! Post your results here!