jpegtran is a libjpeg command-line utility. It allows you to manipulate JPEG files, but its most useful function is optimization.
Installation of jpegtran
For Linux, this utility is usually found in packages:
# apt-get install libjpeg-progs
Usage
For the basic version of optimization, we call the command:
# jpegtran -copy none -optimize -outfile min.image.jpg image.jpg
The abobe command saves the optimized copy to min.image.jpg
-copy none removes all metadata from the source file.
-optimize optimizes image.
Progressive
To change the format to progressive, use the following command:
# jpegtran -progressive -copy none -optimize -outfile min.pro.image.jpg image.jpg
The above command saves the result to the min.pro.image.jpg file.
Quality change
You can also specify the compression ratio to visually select the best value:
# jpegtran -quality 80 -copy none -optimize -outfile min.pro.image.jpg image.jpg
Try different values from 5 to 95.