Steve are you sure that works for shutter count, rather than image numbers which reset after 9,999? I understood that Canon don't put the shutter count in the data so you can't retrieve it easily for several cameras.
I just tried this with a couple of 5D MkII RAW files & the Raw data says ImageNumber 0 on them all.
There is a free programme which will check the shutter count available here:
http://astrojargon.net/40DShutterCou...ookieSupport=1
I think it also works on the 50D