Nautilus Image Converter is a Nautilus extension to mass resize and rotate images. It adds a "Resize Images..." menu item to the context menu of all images. This opens a dialog where you set the desired image size and file name. A click on "Resize" resizes the image(s) using ImageMagick's convert tool. A "Rotate Images..." menu item is also available.
Install Nautilus Image Converter in ubuntu
Open the terminal and run the following command
sudo apt-get install nautilus-image-converter imagemagick