how to get iphone screenshot and save it into iphone photo gallery using unity3d4.0

vuforia concept use unity4.0 and ios6.
my code work for screenshot save in pc but not save iphone photo gallery.
my code:

string screenshotFilename;
				screenshotFilename = Application.dataPath+"/screenshot" + screenshotCount + ".png";
			}while (System.IO.File.Exists(screenshotFilename));

if your concern is to snap shot of iphone any how then press home button of iphone with power button together and it will take screen shot…and don’t know how to do that with script or unity 4.0…