Is there any Mac Application used for part-zooming a picture? I found many screenshots for Mac App Store or iTunes App Store using pictures like this,
I want to find a Mac App can do this work.
This feature is built in ML 10.8 with the accessibility feature zoom. Go to system preferences Accessibility, select zoom the last feature is zoom style select picture-in-picture. This will be a rectangle and follows your mouse any where on screen. You can use option command = (to enlarge) or - (to decrees) the text under the magnifying rectangle, if you have a keyboard with num pad you can use option command + or - for the same effect.