[number] : Optional parameter. Total number of pictures to add in the group pictures.
[layout] : Optional parameter. The index of the layout, which can be obtained according to the figure below. For example, if you want to apply the second layout to 4 pictures, then use
{% grouppicture 4-2 %}{% endgrouppicture %}
It's recommended to use Group Pictures with Fancybox enabled.
Please use absolute paths for <img> inside group pictures. See this issue for details.