You can zoom in on the Picture/Image comparison windows but often I need to zoom in on a specific section where a comparison failed. There is currently no way to "box zoom" where you select a section of the image and zoom straight to it.
Sometimes there are very small differences that I have to zoom in on and it's tedious to use the general zoom and then grab/slide over to where the small difference is.
Below is an example of how it is now. Not too bad but when it's a very small difference it's very tedious to zoom in on a dozen pixels. When I select a box with the current tool, ideally there would be a context menu to zoom to the selection. Or else when you release the box selection it would auto-zoom as happens in tools in the Adobe suite.
http://screencast.com/t/6BQd0JBfUFp0
I'd imagine this would be very trivial for a dev to implement.