You can crop an image from the command-line, using ecconv with the crop option:

ecconv -export tif -compression faxg4 -crop [width][xheight][+/-xoff[+/-yoff]] INFILE OUTFILE

For example to crop a 550 pixels wide and 200 pixels high area at an offset:

ecconv -exp tif -compression faxg4 -crop 550×200+700+550 orig.tif crop.tif

For further information on ecconv options, run:

ecconv -help