Just put this blur view on the imageView. Here is an example in Objective-C:
UIVisualEffect *blurEffect;
blurEffect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleLight];
UIVisualEffectView *visualEffectView;
visualEffectView = [[UIVisualEffectView alloc] initWithEffect:blurEffect];
visualEffectView.frame = imageView.bounds;
[imageView addSubview:visualEffectView];
and Swift:
var visualEffectView = UIVisualEffectView(effect: UIBlurEffect(style: .Light))
visualEffectView.frame = imageView.bounds
imageView.addSubview(visualEffectView)