Error generating images
This is the fix for the issue.

The code taken from duplicated issue in https://stackoverflow.com/questions/36359917/docker-gd-module-for-php-7

Please take this with heaps of grain and salt, and modify the script accordingly.

# Install GD
RUN apt-get install -y libfreetype6-dev libjpeg62-turbo-dev libpng12-dev
RUN docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/
RUN docker-php-ext-install gd


What is actually happens is your GD library is installed BUT without JPEG library configured. Your Drupal will be chill saying GD installed but there is hidden requirement that JPEG need to be exist too.

The line 179 in GDToolkit.php:

$function = 'imagecreatefrom' . image_type_to_extension($this-&gt;getType(), FALSE);


Causes the function imagecreateformjpeg fails to be executed.

Hope it helps someone that confused, cant generate thumbnail with limited knowledge of the errors.

:)