it's definitely 2 different shots as the position of christine's head proves (check the window). chris' hair on her forehead shows changes, too. and - as already mentioned - mick's eyes are looking in slightly different directions.

agreed - no stain! and the window is real - check the crosses' shadows depicted by the sunlight.

But why removing the line and not the flaking areas on the walls? It doesn't make sense.

. . . hmmm . . . i zoomed the colour shot quite a bit - and, well, yes, it may be some sort of "stain" yet. :sorry:
but apart from that i'll stick to everything else i said on this matter.