Installing GD in Docker : <p>I am a complete Docker novice but am having to maintain an existing system. The Dockerfile I am using is as below:</p>

<pre><code>FROM php:5.6-apache

RUN docker-php-ext-install mysql mysqli

RUN apt-get update -y &amp;&amp; apt-get install -y sendmail

RUN apt-get update &amp;&amp; \
    apt-get install -y \
        zlib1g-dev 

RUN docker-php-ext-install mbstring

RUN docker-php-ext-install zip

RUN docker-php-ext-install gd
</code></pre>

<p>When I run 'docker build [sitename]' everything seems ok until I get the error:</p>

<pre><code>configure: error: png.h not found.
The command '/bin/sh -c docker-php-ext-install gd' returned a non-zero code: 1
</code></pre>

<p>What is the cause of this error?</p>
