You need to pass an input file to the program for it to do anything.

imgconv < command.in

See command.in for example. 
Possible commands in a file are:
  i [input filename] [output filename]		-- convert img2bmp
  b [input filename] [output filename]		-- convert bmp2img
  q

You need to end your file with a q (quit) or it will get stuck in an endless loop.