M-JPEG is easily implemented and can be found in cell phones that have a camera installed. Typically low quality and low resolution JPEG images are used to keep the file size down. Since each image is fully self-contained the video can be played back with low overhead. It would be like an MPEG file if all the images were full I-frames.
It is also possible to make motion-JPEG's using the newer JPEG 2000 standard with either lossy or lossless formats. The extension is usually .mjp2 or .mj2. This permits lossless video if needed. It can be used as an archive format for source video.