Not sure about the utility of
...replaced by copies of a single white bitmap...
but I use
ThumbsPlus whenever I need to alter multiple images in the same way. It has a great "batch-process" function for multiple files, allowing easy conversion to/from most image formats; renaming - keeping the old file name, adding a prefix or suffix, numbering options - lots of ; changing image resolution and resizing; image enhancements, cropping etc.
Pretty sure that it'll do what you want. But there's probably a cheaper way to do it in MS-DOS...?!
