How to avoid duplicate image co-ordinates

Hi I have created one application of moving the images.

And i have shown the co-ordinates of images in textbox.

But every time i had seen the co-ordinates by name:- img0(20,40) and when next time i move the same image it shows img0(50,90),due to this in my textbox for same image 2 times co-ordinates are printed.

But i want that when i move image it only replace the co-ordinates.

I mean  if 1st time co-ordinates img0(20,40) then next time in the same img0(70,80) means instead of (20,40) only (70,80) should be printed

no duplicate img0