ImageMagick is a free and open-source software suite for displaying, converting, and editing raster image and vector image files. It can read and write over 200 image file formats.

You can install it on Debian with sudo apt install imagemagick or RHEL with sudo dnf install imagemagick

Convert all images from current folder proportionally.

for file in *.jpg; do convert $file -resize 1000x800 $file; done

for file in *.jpg; do convert $file -resize 1000x800 -quality 95 -rotate 180 -charcoal 4 $file-rotated; done

You can cipher and decipher an image

convert rose.jpg -encipher passphrase.txt rose.png
convert rose.png -decipher passphrase.txt rose.jpg

You need a file containing the passphrase.

There are gems inside like:

How do I read EXIF data

identify -verbose a_nice_photo.jpg

As visual helper you can launch a primitive graphic interface: display Alternatively there is a completely new project: a fork called GraphicsMagick. GraphicsMagick is the swiss army knife of image processing.

Reference Command tools