It depends on the camera, I believe the 1D range enters the number in the exif header file of every picture, so you can get the amount by viewing the exif information. There is a program to do this which you have to pay for, which essential does the same thing when you load an image in to it.
The only cameras I have tried with are the 1Ds Mark II and the 10D, and it is possible to get the value from an image on the 1Ds II, and is not possible on the 10D. I can't remember what other cameras use this method of putting the number of shutter actuations in the image though.