[rareEarth]

I got the iOS version and I was having trouble aligning the corners on the reference object. When I lifted my finger the crosshair would jump slightly with it.

Is it possible to offer edge detection or corner snapping?

I also got much better results when I zoomed as far as possible into the image to align each corner. I think that would be a helpful tip in the app when aligning.

[lubos_]

Good news is that we have recently started playing with corner detection algorithms for snapping, we have first results, it looks promising, after little bit of more work, there might be an update in the near future.