Flask not showing image even though my HTML file can when previewed

Question

This is my sectors.html

{% extends 'layout.html' %}

{% block body %}
  <h1>Sectors Performance</h1>
  <p>
    <img src="../plot.png" width="1000" height="800" alt="graph">
  </p>
{% endblock %}

When I run this essentially standalone, the image loads. But when I run it with the whole Flask app, the image doesn't show. I've also tried having the plot.png in the same folder as the sectors.html file, but can't load when running whole app, but loads if sectors.html run on its own. I'm so confused.

Directory layout:

App_Name  
- templates (folder)  
  - css (folder)
  - includes (folder)
  - js (folder)
  - sectors.html
  - other .html files
app.py
plot.png
sectors.py
other .py files

Thanks