Modulo 100 may sound frightening, but in reality it means just take the two right hand digits. Shutter Count = (folder number-100)*100 + modulo 100 file number.Split the image number into two parts: the last 4 digits (call this file number) and the first three folder number.Thus to convert the image number to the number of shots taken we need to do the following: A twist is that looking at one of the early images I took with this camera is that the folder numbers start at 100 rather than 0. The folders each hold 100 files so the first 3 digits increment once every 100 images to reflect the new folder number while the last 4 digits increase to 9999 then rollover to 0.
Under DCIM there are two folders at present: 291CANON and 292CANON. I then realised that the first 3 digits are in fact the folder number on the memory card. That makes more sense – the last image was IMG_9222.JPG. One EXIF data tool reports the number as 292-9222. On my 10D, it shows 2929222 approaching 3 million shots which is clearly wrong. The number of shutter actuations on older Canon cameras is encoded in the 'Image Number’.
