STIMON.EXE is a windows process that provides extra functionality when you plug in a scanner, digital camera or some type of video/image hardware.

It is called Still Image Monitor and you can read more about it here. Quote:
Still Image Monitor (Stimon.exe) is a tool that is installed by Windows Millennium Edition (Me) and Windows 98 when a Universal Serial Bus (USB) scanning device is successfully enumerated. Stimon.exe is configured to start automatically during the Windows startup process, and is loaded from the following registry key: