How to compress image size in Ubuntu

1. Open the terminal (Ctrl + Alt + T).

2. Install imagemagick by

sudo apt-get install imagemagick

2. Go to the directory of the folder in which you want to reduce the image size.

3. Then type the following command

mogrify -resize 800x * 

Example :

dell@Inspiron:~/Desktop/Image/$ mogrify -resize 800x *