The Mustek's gsmart has the ability to make short video-clips.The file generated is an .avi file, using a codec/decompressor indentifying itself as SP54. The codec will usually be installed by default when you install the bundled software.
Apparently a form of MJPEG but with some internal information missing.
Hardware using this format:
The 'SP' could mean 'Sun Plus', as those hardware use this type of chip.
The only FOURCC really used by this codec seems to be SP44.