GD lib is missing ...

[Svobi]

This fixed it for me adding it to the dockerfile.

RUN apt-get update && apt-get install -y
libfreetype6-dev
libjpeg62-turbo-dev
libmcrypt-dev
libpng12-dev
&& docker-php-ext-install -j$(nproc) iconv mcrypt
&& docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/
&& docker-php-ext-install -j$(nproc) gd

[Jan0707]

Using your fix, I received the following error:

Package libpng12-dev is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'libpng12-dev' has no installation candidate
The command '/bin/sh -c apt-get update && apt-get install -y unzip libfreetype6-dev libjpeg62-turbo-dev libpng12-dev' returned a non-zero code: 100