сделать это невозможно, но мне удалось это сделать, поместив CALayer поверх CAShapeLayer.
это мой код:
CALayer *image =[CALayer layer];
image.frame = CGRectMake(0, 0, 75, 75);
image.contents = (id) [UIImage imageNamed:@"number-1"].CGImage;
[self.layer addSublayer:image];
UIBezierPath *circle = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, 75, 75)];
blueCircleLayer = [CAShapeLayer layer];
blueCircleLayer.path = circle.CGPath;
blueCircleLayer.strokeColor = [UIColor blueColor].CGColor;
blueCircleLayer.fillColor = [UIColor clearColor].CGColor;
blueCircleLayer.shadowColor =[UIColor blackColor].CGColor;
blueCircleLayer.shadowOffset = CGSizeMake(0.0f, 5.0f);
blueCircleLayer.shadowOpacity = 0.7f;
blueCircleLayer.lineWidth = 7.0;
[self.layer addSublayer:blueCircleLayer];