Camera image orientation

In my app I'm capturing images using the Camera. These are being stored in an NSArray as an NSData representation. When I convert the NSData back to the image, the orientation is now landscape instead of portrait as I took it.

    NSData *data = UIImagePNGRepresentation([arrayImage objectAtIndex:0]);
    UIImage *tmp = [UIImage imageWithData:data];

Anyone have an explanation? Thanks.