If you link to an image, the first the first underscore isn't shown in Resource Manager in the Name column.
Example:
Actual filename "0_Cover.tif" - Displays as "0Cover.tif"
Actual filename "0_Back_Cover.tif" - Displays as 0Back_Cover.tif"
Actual filename "appendix_a_header.tif" - Displays as "appendixa_header.tif"