In Plain English: It Doesn't Work
Really, people have been trying to figure out how to get an accurate shutter count for the 20D and 30D for a long time and nobody has found a way to do it other than to use Canon's special software. Why this information is hidden from us on these cameras is a mystery.
If you want to prove that this method does not work, do the following:
First, take a photo using the CF card you've got in the camera now.
Remove that CF card and set it aside. You'll need it later to restore your file numbering to where it is now.
Take a different CF card and using a card reader connected to your PC, delete all files and directories on the card.
Now, insert that card into your camera.
In the Menu, find "File Numbering". Switch that from Continuous to "Auto Reset".
Now, take a photo.
Remove that CF card and put it back into your card reader connected to your PC.
Open that RAW file with the hex editor.
The actual file number is Folder 100, shot 0001 but the decoded Hex will tell you that the number is now 281.
This tells us that first, this location does not show the actual shutter actuations and second, this number cannot be simply decoded as a standard HEX number to even read the file number.
A while back, someone posted the way to properly decode this data to arrive at the current file number on the DPReview 20D forum. I don't remember the details but the main point is that this pair of locations does not give the number of shutter actuations. It only gives you the current file number, and that is easily reset so you never can know what the true shutter count is for a 20D.
Ok, now if you want to get your camera set back to the same shot number as where you left off (more or less), do the following:
Put the card with the 100 0001 shot on it (The shot you just took) back into the camera. Go into the menu and set the File Numbering mode back to "continuous".
Now remove that card.
Install the card we set aside earlier.
Now your camera's numbering will adopt the numbering from that old card and you should be back where you started.
Sadly, nobody that I know of has cracked this mystery...... yet
Jim Posted 38 months ago.