How to return images in flask response?

You use something like

from flask import send_file

@app.route('/get_image')
def get_image():
    if request.args.get('type') == '1':
       filename="ok.gif"
    else:
       filename="error.gif"
    return send_file(filename, mimetype="image/gif")

to send back ok.gif or error.gif, depending on the type query parameter. See the documentation for the send_file function and the request object for more information.