Comparing iOS Screenshots
In the Devices organizer, select the appropriate Screenshots group.
Select two or more screenshots.
Select the Compare option.
Use the Tolerance slider to adjust the comparison threshold.
Compare screenshots to detect subtle changes to your user interface.
The screenshots you select must be the same size and at least somewhat similar. You cannot compare screenshots whose resolution or dimensions are different. For example, you cannot compare a screenshot taken on a Retina display with one taken on a lower-resolution display. If the content of the screenshots is completely different, the Compare option is not available.
© 2012 Apple Inc. All Rights Reserved. (Last updated: 2012-06-11)