[Answer]-Set custom background image in django

What you can do is create another sub block in base template and set background for the parent block. Each page will modify contents of sub-block but not the background.

E.g.

incident/base_report.html

...
{% block main-content-parent %}
  {# code to set background image #}

  {% block main-content %}
  {%endblock%}
{%endblock%}

somepage_template.html

{% extends "incident/base_report.html" %}
{%block main-content %}
   {# your content #}
{%endblock%}