Canon EOS Rebel XTI - Manual (Page 96)

Handy Features
96
The file number is like the frame number on a roll of film. The captured
images are assigned a sequential file number from 0001 to 9999 and
saved in one folder. You can also change how the file number is
assigned.
The file number will appear on the personal computer in this format:
IMG_0001.JPG.
Under the [c] tab, select [File
numbering], then press <0>. Follow
the steps below to select a file
numbering method, then press <0>.
[Continuous]: The file numbering continues in sequence even
after the CF card is replaced.
Even after you replace the CF card, the file numbering continues in
sequence up to 9999. This is convenient when you want to save the
images numbered anywhere between 0001 to 9999 in one folder in
your personal computer.
If the replacement CF card contains images recorded previously, the
file numbering of the new images might continue from the file
numbering of the existing images in the card. If you want to use
continuous file numbering, you should use a newly-formatted CF
card each time.
3 File Numbering Method
0051
CF card -1
0052
CF card -2
File numbering after replacing the CF card
Next sequential file