Documentation can be found at http://www.purl.org/tcl/home/man/tcl8.4/TkCmd/bitmap.htm .
A bitmap is monochromatic representation . Use [which command is for multichromatic?] when you want color images or icons.
"How to edit an executable's desktop icon"
Sometimes people want to know how to edit an X bitmap or to create a new one. See Paul Obermeier's http://www.posoft.de/ 's poBitmap for one tool.
Tk syntax help - Arts and crafts of Tcl-Tk programming Category Command