Displaying *png, *jpg image on a dash app

dash_png.py

import dash
import base64
import dash_html_components as html
from dash.dependencies import Input, Output
import dash_core_components as dcc

app = dash.Dash(__name__)

test_png = r'C:\Users\tashr\Downloads\20190318_114007.jpg'

app.layout = html.Div([
    html.Img(id='img'),
    dcc.Input(id='var1')
    ])

@app.callback(Output('img', 'src'),
              [Input('var1', 'value')])
def dash_img(var1):
    test_base64 = base64.b64encode(open(test_png, 'rb').read()).decode('ascii')
    return 'data:image/png;base64,{}'.format(test_base64)

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