Download on image from another thread(GCD)

dispatch_queue_t downloadQueue = dispatch_queue_create("image", NULL);

    dispatch_async(downloadQueue, ^{

        NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://blogs-images.forbes.com/jasonevangelho/files/2013/01/iphone5.jpeg"]];

        dispatch_async(dispatch_get_main_queue(), ^{

            UIImage *image = [UIImage imageWithData:imageData];

            imageView.image = image;

            imageView.frame = CGRectMake(0, 0, image.size.width, image.size.height);

            scrollView.contentSize = image.size;

        });

    });

    dispatch_release(downloadQueue);