Why are images sometimes not showing in Flask?

Question

Flask

I'm making a site on Flask and the user's page is shown on the photo, he can change the photo and banner, in postgreSQL I save only the file name, and then I make this output

@app.route('/img/<filename>')
def display_image(filename):
    return redirect(url_for('static', filename='avatars/' + filename), code=301)

and in html

src="{{ url_for('display_image', filename=user.profile_pic) }}"

I tried a lot of different options for displaying the image, but all the same. Pictures each does not show different, but rarely shows everything.