So it would be good to have single standard file type for creating a backup image of a bootable flash drive (similar to the .ISO format)
The uses for this would be to be able to use the image to create additional bootable flash drives when the original become corrupt orb the USB flash drive becomes damaged
We do have them and we have them since the dawn of time.
It is called RAW image (or "dd-like") and it is simply (just like the .iso is) a byte by byte (sector by sector) copy of the device.
Usually (though not compulsory) these images have extension .img (or .raw or .dd) and they are nothing "new" or special.
A .iso is a disc (whole disc) image.
A .img is a disk (whole disk) image.
The OFSmount.exe, though a nice tool, is derived from the IMDISK (and from a couple of earlier tools), as such they integrate "less" than other available solutions into a Windows NT.
Olof (the Author of IMDISK) wrote another tool that integrates at a lower level and it is more suited to work with disk images:
and there is another excellent freeware Total Mounter:
You have to uinderstand however how a USB stick is generally a "partitioned" device and NOT a "superfloppy" or a simple volume.
A .iso is instead (usually, i.e. in 99.99% of cases) a simple volume (though it is possible to make hard disk emulation .iso's).
The point is that a .iso file is not really-really flexible because it was designed as a WORM kind of standard (Write Once Read Many) and what most (please read all) the .iso editing utilities actually create on-the-fly a new .iso replacing the original one. (and editing a .iso is never a very good idea when it comes to bootable .iso's), see:
(mind you this does NOT mean that editing a .iso file doesn't work, only that it may not work, particuarly for Windows installs and PE 1.x booting .iso's)
But you are correct that this approach has the advantage that until you add something to the .iso, the .iso is smaller.
A RAW image on the other hand is since day one already as BIG as the device from which it was created.
You could compare this to having a "blank" CD .iso with a fixed size of 650 Mb or so or a blank DVD .iso with a fixed size of around 4.3 Gb, that you can later "fill" with UltraISO or similar (but again this in some cases may cause issues).
There are tens of softwares (freewares or commercial) capable of creating a RAW image from a USB stick, if you like command line I usually recommend the DSFOK toolkit:
but *any* dd port would do:
among the GUI tools, we have Clonedisk:
Still "since the dawn of time", we have managed USB sticks as disk images and viceversa, see also: