https://github.com/rflynn/imgmin
http://www.cyberciti.biz/faq/linux-jpegoptim-jpeg-jfif-image-optimize-compress-tool/
http://www.kokkonen.net/tjko/src/man/jpegoptim.txt
jpegoptim -m82 land_jpegoptim.jpg
pngquant --quality=10-30 butterfly_fly_.png
imgmin butterfly_.png ./butterfly_imgmin.png
overwrite:
pngquant **.png --ext .png --force