This is translated to a PSBOX macro package psboxto command in LaTeX, the first argument being a sizing command and the second a filename.
In HTML mode, the second argument is used to generate a PostScript file reference.
In RTF mode, the second argument is used to find an RGB-encoded Windows bitmap file and insert it in the output file. The file must be RGB-encoded; RLE-encoded files don't seem to work. Note that this facility has not been rigorously tested.