How does one display a screen shot for example, on a iPhone in portrait mode, so it's somewhat clear to view ? My only solution is to make the resolution extremely high so they don't have to zoom & pan ?
Your sulution won't solve that problem. It will only makes the filesize too large and thus slow with loading. If your screenshot is fluid and therefore gets resized, so it fits in lets say 320px, then they still have to zoom & pan.