Canon 430 - Manual (Page 90)

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About File Numbers and Folder Numbers
Images are assigned file numbers from 0001 to 9900, and folders are
assigned folder numbers from 100 to 998 (Folder numbers cannot
contain 99 in the last two digits).
Folder File Capacity
Each folder usually contains up to 100 images.
However, since images shot in continuous shooting and stitch assist
are always saved into the same folder, a folder may contain more than
100 images. The number of images may also exceed 100 if a folder
contains images copied from a computer or images shot with other
cameras. Please note, however, that the images in folders containing
2001 or more images cannot be played back in this camera.
Folder numbers cannot contain 99 in the last two digits