如何在Flask中上传和显示图像

Question

我尝试上传并在我的模板html上显示图像。当我上传图片时，我获得了成功。但是当我想显示图像时，服务器会说：＆＃34;得到静态404＆＃34;

有人可以帮忙吗？

#views.py 
@app.route("/upload/<username>", methods=['GET', 'POST'])   
@login_required  
def upload(username):   
    form = PhotoForm()   
    user = User.query.filter_by(username=username).first()  
    if request.method == 'POST' and form.validate_on_submit():      
        f = form.photo.data         
        filename = secure_filename(f.filename)
        f.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))         
        return redirect(url_for ('user', username=user.username, filename=filename, f=f))    
    return render_template("change_profile_picture.html",form=form)
 #user.html  <img src="{{ url_for('static', filename=filename) }}">****