/* Action taken when the "Save" button (saveAsImageButton) is pressed in the app */
- (IBAction)saveScreenshot {

   // Define the dimensions of the screenshot you want to take (the entire screen in this case)
   CGSize size =  [[UIScreen mainScreen] bounds].size;

   // Create the screenshot
   UIGraphicsBeginImageContext(size);
   // Put everything in the current view into the screenshot
   [[self.view layer] renderInContext:UIGraphicsGetCurrentContext()];
   // Save the current image context info into a UIImage
   UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();

   // Save the screenshot to the device's photo album
   UIImageWriteToSavedPhotosAlbum(newImage, self,
      @selector(image:didFinishSavingWithError:contextInfo:), nil);
}

// callback for UIImageWriteToSavedPhotosAlbum
- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo {

   if (error) {
       // Handle if the image could not be saved to the photo album
   }
   else {
      // The save was successful and all is well
   }
}

Note: The bulk of these functions are out of Apple’s UIKit framework so check out their documentation for even more information.