The UIScrollView is used to view a content whose size is larger than the screen of the device. It can also be used to zoom in and zoom out an image, or to view an image that is significantly larger than the screen of the device. To make the scroll view zoom in and zoom out an image, follow the steps as given below.

- (void)viewDidLoad
{
    UIScrollView *scroll = [[UIScrollView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]];
    scroll.backgroundColor = [UIColor blackColor];
    scroll.delegate = self;
    image = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image.JPG"]];
    scroll.contentSize = image.frame.size;
    [scroll addSubview:image];

    scroll.minimumZoomScale = scroll.frame.size.width / image.frame.size.width;
    scroll.maximumZoomScale = 2.0;
    [scroll setZoomScale:scroll.minimumZoomScale];

    self.view = scroll;
    [scroll release];

}

- (CGRect)centeredFrameForScrollView:(UIScrollView *)scroll andUIView:(UIView *)rView
{
    CGSize boundsSize = scroll.bounds.size;
    CGRect frameToCenter = rView.frame;

    // center horizontally
    if (frameToCenter.size.width < boundsSize.width) 
{
        frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2;
    }
    else {
        frameToCenter.origin.x = 0;
    }

    // center vertically
    if (frameToCenter.size.height < boundsSize.height) 
    {
        frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2;
    }
    else 
    {
        frameToCenter.origin.y = 0;
    }

    return frameToCenter;
}

#pragma mark UIScrollViewDelegate

- (void)scrollViewDidZoom:(UIScrollView *)scrollView 
{
   image.frame = [self centeredFrameForScrollView:scrollView andUIView:image];;
}

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView 
{
    return image;
}