XOR combining of image and CutBrush stamp

[Svengali]

A question for programmers:

At a time when color lookup tables were used, I remember there being a way of testing the difference between two images by using XOR when combining image A with image B. If the resulting image C was BLANK, then Image A and Image B were EXACTLY the same.

I'm trying to do something similar in a script I am working on... I want to compare two images to see if the original has changed. One thing I've tried is to copy image A to another layer creating image B. Then, comparing the two images after applying some process to the original image. For this, I am using the command:
tv_layercompareimage iLayerId1 iImage1 iLayerId2 iImage2 which results in a 0 or 1 (no difference vs difference).
This involves creating a temporary layer, copying image A to the second layer, doing a process, then comparing the two images... and depending on the result, applying option A or option B (after deleting the temporary 2nd layer).

So, I guess my question is: Is there a simpler, faster method in GEORGE to do this "before/after" comparison of two images??? Or simply detecting if an image has changed? Perhaps using the PixelMatrix command or Custom Mode combined with a CutBrush copy of the original Image A?

Thanks for any help (from anyone!)

Sven