I have gone through Apple docs about UITableView class and delegate reference but couldn\'t find the way to set the table header height explicitly.
I set Table cell
You can create a UIView with the desired height (the width should be that of the UITableView), and inside it you can place a UIImageView with the picture of the proper dimensions: they won't stretch automatically.
You can also give margin above and below the inner UIImageView, by giving a higher height to the container view.
Additionally, you can assign a Translation transform in order to place the image in the middle of its container header view, for example.