I am trying to set "myimage" as the background for my GUI but having problems with

self.canvas.create_image(myimage,750,450)

def __init__(self):
        self.root=tk.Tk()
        # The number of times the GUI is updated
        self.ctr = 0
        #creating the Canvas
        self.canvas = tk.Canvas(self.root, width=750, height=450, bg = "black")
        #Sets the background as an image
        myimage=PhotoImage(file='world.gif')
        self.canvas.create_image(myimage,750,450)