在图像上绘制对比字符串

So, I have a snapshot of a video source, which I get into an Image, grab a Graphics object for it, and then draw a timestamp in the bottom right of the image. No problem thus far. However, I cannot guarantee what colour is going to be behind the text, so no matter what brush I use, it will almost certainly clash with some of the images that it is drawn on, making the text unreadable.So, I have a snapshot of a video source, which