Not sure if this will work on other Android phones from Samsung, but here’s a rather simple way to take a screenshot of whatever is on the screen of your Galaxy SIII:

First, make sure that the use “Palm swipe to capture” option is enabled in the “Hands motion” section under Settings –> Motion. Once enabled, you can take a screenshot simply by swiping the side of your hand across the screen from right to left or left to right. Although the gesture is called a palm swipe, you want to use just the edge of your hand – not unlike the motion you would use to brush crumbs off a table.

How to take a screenshot on the Samsung Galaxy S3 (free – no app required!)