Often one has to crop excess margins from an raster image. Common image graphical editors have autocrop tool, but if many files need to be processed, opening and saving files one by one quickly becomes tedious.
A better solution is to use convert tool that is a part of the powerful Imagemagick toolkit:
convert image.jpg -trim -bordercolor White -border 20x10 +repage cropped_image.jpg
This command reads the original file, removes (trims, crops) white borders, adds 20 pixel white borders horizontally and 10px vertically, and stores the file as cropped_image.jpg.
It is also possible to process all image files in the current directory with the following one line command:
for i in `ls *.jpg`; do convert $i -trim -bordercolor White -border 20x10 +repage cropped_`basename $i`; done
If you want to convert to another image format, it can be done conveniently at the same time (-quality option controls the jpg quality):
for i in `ls *.gif`; do convert $i -trim -bordercolor White -border 20x10 -quality 92 +repage cropped_`basename $i gif`jpg; done
Above basename utility is used for trimming suffix from the file name.
Pebbles in the Sand 