Just some of my thoughts:

If you want scalability, you probably won't be satisfied with a photograph... Unless you have it in good resolution and use QPainter::SmoothPixmapTransform, but even though I think that the 'numbers' would not look very good.
I would probably draw the clock in a small app on a QPicture (using various shapes) and save it then (as done here). You can then use and load the QPicture easily in your clock application and resize it without loosing quality...