__block UIActivityIndicatorView *activityIndicator =    [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:activityStyle];
activityIndicator.center = imageView.center;
activityIndicator.hidesWhenStopped = YES;
[imageView setImageWithURL:[NSURL  URLWithString:@"http://www.domain.com/path/to/image.jpg"]
           placeholderImage:[UIImage imageNamed:@"placeholder.png"]
                    success:^(UIImage *image) { [activityIndicator removeFromSuperview]; }
failure:^(NSError *error) { [activityIndicator removeFromSuperview]; }];

[imageView addSubview:activityIndicator];
[activityIndicator startAnimating];