By combining UIGraphicsBeginImageContext() and -renderInContext in CALayer, you can draw contents into a image (UIImage) object. It is like screen capture.
UIGraphicsBeginImageContext(view.frame.size);
[view.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CGContextTranslateCTM() modifies the x- and y- coordinates (otherwise it starts from (0,0)). By using CGContextTranslateCTM(), you can change the start capturing point so that it can capture limited area in the UIScrollView content.
CGSize pageSize = CGSizeMake(320, 480);
int currentPage = 2;
UIGraphicsBeginImageContext(pageSize);
CGContextRef resizedContext = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(resizedContext, 320 * currentPage, 0);
[scrollView.layer renderInContext:resizedContext];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();