Remove image background with tkinter

I'm trying to make two layers with two images in which the background stays entire in the application, and the second layer overlaps. The second is transparent, however, when the display occurs, it places gray background. How can I get this fund?

from tkinter import *
import time
janela = Tk()

janela.geometry("1920x1080")
janela.title("Mario")

mario = PhotoImage(file = "cenario.png")

label = Label(janela, image = mario).place(x=0,y=0)
photo = PhotoImage(file = "mario.png")
label = Label(janela, image = photo).place(x=3,y=600)

janela.mainloop()