Presetting the file-counter to any desired number NNNN for the first picture to be taken:
For example you want to start with a session and the first file should start with "Img-5000.jpg".

* Put a file on the card with a name: "Img-(NNNN-2).jpg". For this example: "Img-4998.jpg".

* The folder name should be set to the filename: "1NNcanon". For this example: "149canon".

* Insert this card into the camera. Don't take a picture yet.

* In the menu select the 3th TAB, Item 5, "Filenr.". Set it to "Auto reset".

* Take a picture now.

* Select the menu again and reset "Filenr." back to "Continue".

The card contains the new picture with filename "Img-(NNNN-1).jpg". For this example: "Img-4999.jpg". The next picture will be the desired number. For this example: "Img-5000.jpg".