Here's some tips on using SmartFlybox.
"Placing" a fly entails tagging the fly in the image. To tag a fly, choose the "Place a Fly" action item. Then touch the fly in the image - you will then need to select the fly from the fly catalog.
You can use two fingers to zoom in and out in the image.
You can double-tap with a finger to zoom in and out as well.
You can touch and hold to locate a point accurately using a magnifying glass concept: