How to crop white margins from photo and fax?
Use option "Crop method:margins" to crop white margins. Margins color is specified in brackets, letters mean channels: R - red, G - green, B- blue.
margins - this parameter specifies that the number of pixels set in size parameter shoud be cropped from every side of the image.
The program will automatically find on image a rectangle containing pixels with color different from color specified in "Crop method:margins" option. After this it will crop the margins. If you don't know how to find out numeric color code, read this section.