Sometimes I know that the content of the page will differ, but the layout should still be the same. In cases like that I would like to be able to specify which area of the page to compare and which to ignore.

One way to achieve this is to allow the user to specify a "mask" image with black pixels corresponding to regions to compare and white corresponding to regions to ignore.

Another alternative is to just let user specify coordinates of regions that matter (or regions to ignore) directly.

How feasible would this be? Thanks