Identify the LCD and find the dead pixel

Hi,

I'm so new to this vision assistant. I'm having a trouble finding the dead pixels in LCD screen. Here is what I'm trying to do

1) I'm capturing an images of LCD screen with different lights  (Red, Green and Blue LCD lights) each time from camera .

2) First I'm using the image mask to select that particular LCD region

3) Then I'm using the Color panel extraction with HSV value panel to convert to any LCD color screen to gray

4) and using the quantifier and finding the mini value (if it is zero then it has dead pixel)

Issue is LCD screen position changes in every image.  How I can identify or detect that LCD screen wherever it is on the image.