import turtle
import random

t = turtle.Turtle
s = turtle.Screen()

img1 = "smile"
img2 = "back"

s.addshape(img1)
s.addshape(img2)

a = random.randint(1,10)
b = random.randint(1,10)

print(a, "+" , b, "=")

x =input()
c = int(x)

if a+ b == c:
    print("정답입니다.")
    t.shape(img1)
else:
    print("틀렸습니다. 정답은"+str(a+b)+"입니다.")
    t.shape(img2)

이렇게 코드를 짰는데요,

Traceback (most recent call last):
  File "C:/Users/asd/Desktop/교재 코드 모음/chapter06/6-8 산수문제못ㄱ.py", line 12, in <module>
    s.addshape(img1)
  File "C:\Users\asd\AppData\Local\Programs\Python\Python38\lib\turtle.py", line 1135, in register_shape
    raise TurtleGraphicsError("Bad arguments for register_shape.\n"
turtle.TurtleGraphicsError: Bad arguments for register_shape.
Use  help(register_shape)

이렇게 오류가 뜨는데 뭘 고쳐야 할까요??