python里添加图片怎么无法显示

帮忙看看这段代码有什么问题，运行之后也不报错，就是不显示图片，图片路径是没有问题的

 import tkinter
from tkinter import *
import tkinter as tk
class Application(tk.Frame):
    def __init__(self, master=None):
        tk.Frame.__init__(self, master)
        self.pack()
        self.createWidgets()
    def createWidgets(self):
        photo = PhotoImage(format="gif",file="./material/setting.gif")
        imgLabel = Label(self, image=photo)
        imgLabel.pack(side=RIGHT)
root = tk.Tk()
app = Application(master=root)
app.mainloop()