How do I check for a win in a tic tac toe game?

I've seen how to check for a win on tic tac toe games, but I am using images and I can't seem to figure out how. I thought of using if statements and having 3 buttons equal the image that is shown, but that doesn't seem to work. Any ideas?

from tkinter import*

#Window stuff   
window = Tk()
window.title("Tic Tac Toe")
window.configure(background = "black")
window.geometry("400x400")

#Variables
global clickable
playerXturn = True

#Display X or O
def buttonClicked(c) : 
    global playerXturn
    if playerXturn == True :
        buttonList[c]["image"] = picX
        playerXturn = False
        labelTurn ["text"] = "O's turn"

    elif clickable[c] == "" : 
        buttonList[c]["image"] = picO
        playerXturn = True
        labelTurn ["text"] = "X's turn"
#Check for a win
    if button1 == picX and button2 == picX and button3 == picX:
        print("r") 

#Images
picX = PhotoImage (file = "x.gif") 
picO = PhotoImage (file = "o.gif")
picBlank = PhotoImage (file = "sw.gif") 

#Buttons
button1 = Button (window, text = "", image = picBlank, command = lambda: buttonClicked(0))     
button1.grid (row = 0, column = 0)
#button1["state"] = DISABLED 
button2 = Button (window, text = "", image = picBlank, command = lambda: buttonClicked(1))    
button2.grid (row = 0, column = 1)
#button2["state"] = DISABLED 
button3 = Button (window, text = "", image = picBlank, command = lambda: buttonClicked(2))  
button3.grid (row = 0, column = 2)
#button3["state"] = DISABLED 
button4 = Button (window, text = "", image = picBlank, command = lambda: buttonClicked(3))   
button4.grid (row = 1, column = 0)
#button4["state"] = DISABLED 
button5 = Button (window, text = "", image = picBlank,  command = lambda: buttonClicked(4)) 
button5.grid (row = 1, column = 1)
#button5["state"] = DISABLED 
button6 = Button (window, text = "", image = picBlank,  command = lambda: buttonClicked(5))  
button6.grid (row= 1, column = 2)
#button6["state"] = DISABLED 
button7 = Button (window, text = "", image = picBlank, command = lambda: buttonClicked(6)) 
button7.grid (row = 2, column = 0)
#button7["state"] = DISABLED 
button8 = Button (window, text = "", image = picBlank, command = lambda: buttonClicked(7))   
button8.grid (row = 2, column = 1)
#button8["state"] = DISABLED 
button9 = Button (window, text = "", image = picBlank, command = lambda: buttonClicked(8))  
button9.grid (row = 2, column = 2)
#button9["state"] = DISABLED 

#Labels
labelTurn = Label (window, text = "",) 
labelTurn.grid (row = 4, column = 4)

#Lists
buttonList = [button1, button2, button3, button4, button5, button6, button7, button8, button9]
clickable = ["", "", "", "", "", "", "", "", ""]

window.mainloop()