What should I do to load my images with D3-Graphviz and Flask?

Question

I am trying to load my files that I have defined on a JavaScript file (with D3-Graphviz) to a Flask server. Here is my current server structure:

static
   --images
      --File.png
      --Actor.png
      --System.png
      --Service.png
      --background.jpg
   --style.css
   --visualisation.js
templates
   --website.html

Here is my current code to implement the graph (with icons) in visualisation.js:

let graph = d3.select("#graph")
let newgraphviz = graph.graphviz()
newgraphviz.transition(function () {
      return d3.transition("main")
          .ease(d3.easeLinear)
          .delay(500)
          .duration(1500);}
  )
  .on("initEnd", render)
  .on("end", draw_edges);

let graph2 = graph.selectAll(".edge").nodes()
console.log(graph2)
function draw_edges() {
  graph.selectAll(".edge")
  .nodes()
  .forEach(function (e, i) {
    setTimeout(() => {
      {
        let ee = d3.select(e);
        ee.select("path")
          .attr("stroke-width", 1)
          .transition()
          .duration(800)
          .attr("stroke", "red")
          .attr("stroke-width", 2);
        ee.select("polygon").transition().duration(800).attr("fill", "red");
      }
    }, 800 * (i + 1));
  });
  }

function renderString(str){
    newgraphviz.tweenShapes(false)
     .addImage("{{ url_for('static', filename='images/Actor.png') }}", "50px", "50px")
     .addImage("{{ url_for('static', filename='images/File.png') }}", "50px", "50px")
     .addImage("{{ url_for('static', filename='images/System.png') }}", "50px", "50px")
     .addImage("{{ url_for('static', filename='images/Service.png') }}", "50px", "50px")
    .renderDot(str, function() {
      graph.selectAll("title").remove();
      graph.selectAll("text").style("pointer-events", "none");
    });
    
}
// This would be used to render the GV file.
function render(filename) {
fetch(filename).then(response  => response.text()).then(textAsString => 
     renderString(textAsString));
}

And here is my code (in Flask) for deploying the website:

from flask import Flask, render_template, request, jsonify
import subprocess

app = Flask(__name__, static_url_path='/static')

@app.route('/')
def index():
    return render_template('website.html')

if __name__ == '__main__':
    app.run(debug=True)  

However, when I run this Python file to run the website.html file, I could not get the icons (File.png, Actor.png, System.png and Service.png) displayed in the graph, although my background.png file (that I defined in the CSS file) could still be loaded.

So, is the problem in my code related to D3-Graphviz, or just a problem about loading images in Flask? And what should I do to resolve this problem?

Update: From what I read in Flask, I have changed the addImage function to .addImage("{{ url_for('static', filename='images/System.png') }}", "50px", "50px"), however this does not seem to solve my problem.