These pictures are a representation of the 3 step process I often use when making original 2d game images. I am very fond of 2d games as they let you create enticing new concepts and twists without a lot of manpower that I expect these 3d, more robust, games to take. The process is as follows:

1. Draw images by hand (or use some tool on the computer)

2. After scanning my drawn images, I crop out each individual frame and touch it up by adding the colors and smoothing out any details I need. I need to make sure the frames all are inside an imaginary box where the box dimensions are such that the biggest frame just barely fits inside. I then place the boxes side by side with one frame per box in the appropriate order. This step is by far the majority of the work unless you are bad at drawling like me.

3. The result of step 2 is what 2d games refer to as a "sprite sheet," which is a big image of every individual frame the game needs. The programmer may need to create his own animation algorithm that fetches and uses each frame in the way the final product was envisioned. However, if you are comfortable with the GIF libraries that many 2d engines support than you can animate the frames yourself using some image processing tool (I use GIMP). The result of step 3 is the third animated image you see above.