You can take high resolution screenshots by using the button showed in this screenshot, it basically combines 9 zoomed in screenshots to a big one.
I think there was a way to make it combine more, like 16 or 25, but I'm not sure, and now I can't remember where to set it, if it's possible... 9 shouldn't be enough to get 50+ megapixels, except if you have a very big resolution!