So far I have not written an application that displays an image. So I don't know how to handle images.
But if I search in Qt Assistant for a rotate() method it is offered in five different classes (e.g. QGraphicsItem or QPainter).
If none of them is useful you probably have to implement are rotate method yourself. Or rotating is possible with this method: http://doc.trolltech.com/4.4/qimage.html#transformed.