MakeIcon

MakeIcon is a command line utility, that converts images in
.GIF, .BMP and also .ICO file formats into Windows icons
with desired number of bits per pixel: 1, 4, 8, 16, 24, 32
bits supported.

You can use arguments on command line to
specify desired number of bits per pixel and a transparency
color number for destination icon file. Also it can create
text-mode color images for console.