Use option "method:autocrop color" to crop white margins. Margins color is specified in brackets, letters mean channels: R - red, G - green, B- blue.
Example*:
ICPCL.exe –convertto jpg –source " C:\Images\*.*" –dest "C:\out\" -oper Crop method:autocrop color:"r:255,g:0,b:0,a:100"
The program will automatically find on image a rectangle containing pixels with color different from color specified in "-acropm" option. After this it will crop the margins.
* This example works the same way with other support formats.