finding client screen res

In my continuing web site revamp, I am adding a faded picture as a background - but in watermark mode so that it does not scroll up or down. The problem is, if the client screen resolution is set higher, then the picture starts repeating itself - making it look ugly. I am sure it is possible to read in the client's screen res and thus I could provide a picture background that would fit perfectly.

Any thoughts or feedback very welcome, or is this a naff idea?

Thanks

Nathan

One of the problems with designing for screen res is that many people don't run their browsers full screen. Even when they do, you have to accommodate scroll bars, various numbers of link bar rows, etc.

The css solution would be best.