Windows only: Free utility CombineZM uses a image technique called focus stacking to combine multiple photos together, allowing for a wider depth of field, and clear, sharp images — a useful technique for getting great close-up photography.
Photos by Brian Valentine.
Photography site WonderfulPhotos.com has a step-by-step tutorial on stacking multiple images to create an all-around focused photo using CombineZM. The program can automatically combine these photos, but if you like a little more control, it also allows you to manually align them for a cleaner picture.
Focus stacking is more commonly used in macro-photography, and is done by taking at least three photos of the same object. The photos must focus on different parts of the object, with at least one each on the foreground, middleground, and background. By combining photos with different focuses, CombineZM will create an all-around sharp picture; more than what's possible on your camera.
CombineZM is a free program available for Windows only.