i am having difficulty in grid management and image changes in tkinter

I want to build a rock paper scissor game. and its GUI using tkinter and python.but the output is messed up.
ps. I am not from cs background I am from biology background, just started to learn python as a hobby.
the images overlap each other, and the column sizes are not proper. how to fix these.

from tkinter import *
import random
from PIL import ImageTk , Image
main = Tk()
###main window position###
main_width = 700
main_height = 570
screen_width = main.winfo_screenwidth()
screen_height = main.winfo_screenheight()
xpoint = (screen_width/2) - (main_width/2)
ypoint = (screen_height/2) - (main_height/2)
main.geometry("%dx%d+%d+%d" %(main_width, main_height, xpoint, ypoint))
main.title("Rock,Paper,Scissor game")
back = ImageTk.PhotoImage(Image.open("mainbg2.jpg"))
backimg = Label(main, image = back).grid(row = 2, columnspan =4)
##the problem here is the backimg is not replace by the 2 new images of player and computer hand, it just is overlapped by them.###
###usefull variables###
rockimg = ImageTk.PhotoImage(Image.open("rock.gif"))
scissorimg = ImageTk.PhotoImage(Image.open("scissor.gif"))
paperimg = ImageTk.PhotoImage(Image.open("paper.gif"))
###button actions###
def rock(y):
rocklabel = Label(main,image= rockimg )
rocklabel.grid(row=2, column=0, columnspan = 2, sticky = W)
rocklabel.image=rockimg
game(y)
def paper(y):
paperlabel = Label(main, image = paperimg)
paperlabel.grid(row=2, column=0,columnspan = 2,sticky = W)
paperlabel.image = paperimg
game(y)
def scissor(y):
scissorlabel= Label(main, image = scissorimg)
scissorlabel.grid(row=2, column=0, columnspan = 2,sticky = W)
scissorlabel.image = scissorimg
game(y)
###main logic###
x=[ rockimg, paperimg, scissorimg]
def game(y):
##computer hand print##
intial= random.choice(x)
##formula##
value= y - x.index(intial)
###the problem here is the player hand image and computer hand image are too wide apart###
output= Label(main, image = intial).grid(row=2, column=2, columnspan=2)
if value==2 or value == -1:
lost = Label(main, text = " You lost").grid(row = 4, column= 0)
elif value == 1 or value == -2:
win = Label(main, text = " You win").grid(row = 4, column= 0)
else:
tie = Label(main, text = " It's a tie").grid(row = 4, column= 0)
###buttons and labels###
###the problem here is the arrangement of the rows and columns is not pretty, the spacing between the buttons is messedup###
mainheading = Label(main, text = 'Rock Paper Scissor game', padx = 4, pady = 7, width=20)
mainheading.grid(row = 0, column = 0, columnspan = 4)
rock_button = Button(main, text = "ROCK",  command = lambda:rock(0) , height = 2 ,width = 23)
rock_button.grid(row = 4, column = 0 ,  sticky = W+E, padx = 25)
paper_button = Button(main, text = "PAPER",  command = lambda:paper(1), height = 2 ,width = 23)
paper_button.grid(row = 4, column = 1,sticky = W+E , )
scissor_button = Button(main, text = "SCISSOR",  command = lambda:scissor(2), height = 2 ,width = 23)
scissor_button.grid(row = 4, column = 2,sticky = W ,)
exit_button = Button(main, text = "exit" , command = main.destroy).grid(row = 5 , column = 3)
main.mainloop()

if all you want to do is remove the old labels then grid_forget() is probably all you need to do. I added a fifth column so that it looked a bit better to me, if your images are the same size, the resizing due to the text length difference will disappear. You could also also use the config method just like with text but I personally prefer the idea of creating the image instance then just using grid_forget method.

sample code (i replaced your images with text since i don't have them):

###I brought the label creation out of the function, replace with your images###
rocklabel = Label(main, text = 'ROCK')
#rocklabel = Label(main,image= rockimg )
#rocklabel.image=rockimg
paperlabel = Label(main, text = 'PAPER')
scissorlabel= Label(main, text ='SCISSOR')
###a set for opponent images also, replace text with your images###
oppRock = Label(main, text = 'ROCK')
oppPaper = Label(main, text = 'PAPER')
oppScissor= Label(main, text ='SCISSOR')
###placeholder images for initial game window###
inilabel = Label(main, text = "Let's play!")
inilabel.grid(row=2, column=1)
output= Label(main, text = 'Opponent')
output.grid(row=2, column=3)
result = Label(main, text = 'Result')
result.grid(row = 5, column= 0, columnspan=5, pady = 10)
###button actions, now you can call grid forget method on the created labels###
def rock(y):
paperlabel.grid_forget()
scissorlabel.grid_forget()
rocklabel.grid(row=2, column=1,)
game(y)
def paper(y):
rocklabel.grid_forget()
scissorlabel.grid_forget()
paperlabel.grid(row=2, column=1)
game(y)
def scissor(y):
rocklabel.grid_forget()
paperlabel.grid_forget()
scissorlabel.grid(row=2, column=1)
game(y)
###main logic###
x=[ 'ROCK', 'PAPER', 'SCISSOR']
def game(y):
##computer hand print##
inilabel.grid_forget()
intial= random.choice(x)
##formula##
value= y - x.index(intial)
output.config(text = intial)
###accounting for the random choice, add appropriate opp image###
if intial == 'ROCK':
oppPaper.grid_forget()
oppScissor.grid_forget()
oppRock.grid(row=2, column=3)
elif intial == 'PAPER':
oppRock.grid_forget()
oppScissor.grid_forget()
oppPaper.grid(row=2, column=3)
else:
oppRock.grid_forget()
oppPaper.grid_forget()
oppScissor.grid(row=2, column=3)
###use config options on a text change rather than new object###
if value==2 or value == -1:
result.config(text = " You lost")
elif value == 1 or value == -2:
result.config(text = " You win")
else:
result.config(text = "It's a tie")
###buttons and labels###
mainheading = Label(main, text = 'Rock Paper Scissor game', padx = 4, pady = 7, 
width=20)
mainheading.grid(row = 0, column = 0, columnspan = 5)
rock_button = Button(main, text = "ROCK",  command = lambda:rock(0) , height = 2 
,width = 23)
rock_button.grid(row = 4, column = 0)
paper_button = Button(main, text = "PAPER",  command = lambda:paper(1), height = 2 
,width = 23)
paper_button.grid(row = 4, column = 2)
scissor_button = Button(main, text = "SCISSOR",  command = lambda:scissor(2), height 
= 2 ,width = 23)
scissor_button.grid(row = 4, column = 4)
exit_button = Button(main, text = "exit" , command = main.destroy).grid(row = 6 , 
columnspan = 5, pady=10)