Web application with video streaming and dynamic data through ajax and flask

I am trying to add dynamic data updater to my video-streaming web interface. I use flask framework. For data updater I use ajax. If I comment <img id="bg" src="{{ url_for('video_feed') }}">line in index.html, all right, I received current time (_get_time) from python and change it in html #result block. But with <img id="bg" src="{{ url_for('video_feed') }}"> line, I doesn't receive time from python. #result block in html doesn't update.

main.py:

from flask import Flask, render_template, Response, jsonify, request
from camera import VideoCamera
from datetime import datetime

app = Flask(__name__)

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

def gen(camera):
    while True:
        frame = camera.get_frame()
        yield (b'--frame\r\n'
           b'Content-Type: image/jpeg\r\n\r\n' + frame + b'\r\n\r\n')

@app.route('/video_feed')
def video_feed():
    return Response(gen(VideoCamera()),
                mimetype='multipart/x-mixed-replace; boundary=frame')

@app.route('/_get_time')
def get_time():
    time = datetime.utcnow()
    return jsonify(result=time)

if __name__ == '__main__':
    app.run(host='0.0.0.0', debug=True)

index.html :

<html>
    <head>
        <title>Video Streaming Demonstration</title>
        <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1 /jquery.min.js"></script>
        <script>window.jQuery || document.write('<script src="{{url_for('static', filename='jquery.js') }}">\x3C/script>')</script>
        <script type=text/javascript>
            $SCRIPT_ROOT = {{ request.script_root|tojson|safe }};
        </script>
        <script type=text/javascript>
            setInterval("add()",1000)
            function add ()
            {
                $.getJSON($SCRIPT_ROOT + '/_get_time',
                function(data) {
                    $("#result").text(data.result);
                });
            }
        </script>
    </head>
    <body>
        <h1>Video Streaming Demonstration</h1>
        <img id="bg" src="{{ url_for('video_feed') }}"><!--Comment it -->
        <span id=result>?</span>
    </body>
</html>

Thank you!