In to the terminal type as following

sudo apt-get install nautilus-image-converter

then type your password

There are many option for you to choose

Image Size

 - Select a size : to choose the size in the selection menu.

 - Scale : to resize the image size to how many percent of the original size.

 - Custom size : to fix the size by fix the width and height (this option will not crop the image).

Filename

 - Append : to rename the resized image name following with the text in the textfield.

 - Resize in place : to replace the resized image with the original image.