A useful method to mask a view according to an alpha channel to an image. Example usage: place the masking image using IB (make it hidden), and dynamically create a view around it, that you mask using this method.

gistfile1.m

+ (void)maskView:(UIView *)targetView withImageView:(UIImageView *)maskingImageView {
    CALayer *maskingLayer = [CALayer layer];
    maskingLayer.frame = CGRectMake(maskingImageView.frame.origin.x - targetView.frame.origin.x,
                                    maskingImageView.frame.origin.y - targetView.frame.origin.y,
                                    maskingImageView.frame.size.width,
                                    maskingImageView.frame.size.height);

    maskingLayer.contents = (id)maskingImageView.image.CGImage;
    targetView.layer.mask = maskingLayer;
}