As a practical concern, I think you are worried that if you have image patch A and are trying to match it to other image patches in a photo, that it may have a large correlation to a nearly constant patch B, which it does not resemble. As far as I know, that might happen.

I'm sure your next question is whether there is some modification of the correlation formula that would produce a function that would avoid this problem. Off hand, I don't know of one. I'll have to think about it.