Well, the most common application (tool) that I use in Linux for quick resizing an image is imagemagick an cmd based tool
The best 2 commands that I use most are:
Resizing just an image we use (convert):
This command actually takes image.jpg and resizes it on 500×500 pixels but it depends on the real size image so if it’s 600×500
the command wont deform its shape and make it like a square, but it’ll make it exc 500×400
# sudo convert image.jpg -resize 500x500 *.jpg
Resizing all images in a folder we use (mogrify):
When using mogrify its important to tell the path of images.
# sudo mogrify -path /home/user/yourimagesfolder/ -resize 500x500 /home/user/yourimagesfolder/*.jpg
Altin Ukshini 