install php70-gd on ubuntu

just try

sudo apt-get install php7.0-gd 

i got it working that way. Greetings.

PHP7 packages for Ubuntu including php7.0-gd can be installed via PPA for PHP by Ondřej Surý:

sudo add-apt-repository ppa:ondrej/php
sudo apt-get update

Next, install the desired version:

sudo apt-get install php7.0-gd
# or
sudo apt-get install php7.1-gd
# or
sudo apt-get install php7.2-gd
# or
sudo apt-get install php7.3-gd
# or
sudo apt-get install php7.4-gd

EDIT:

As MacroMan stated, under Ubuntu 16.04 you don't need to add the repository any more. Simply issuing sudo apt-get install php7.0-gd works.

In 2018, there is an alias package for this:

sudo apt-get install php-gd

Use this to retrieve the last version.

my php version is 7.1

sudo apt-get install php7.1-gd

this command is work for me