I wrote a downloaded image to my removable drive, now Windows says it is corrupted

I get this quite often, either in questions, bug reports, direct emails, reviews, etc.

The problem is not with Win32ImageWriter (aka Win32DiskImager). This utility reads and writes at the raw device level. If the device being read is completely blank (and no filesystems or partitions exist on it), the resulting image would indeed be considered garbage, or likely just a file full of zeros. If an image were created from a 512M flash drive and then written to a 16G flash drive, Windows (and any other OS) would see the resulting filesystem as 512M. This utility does not have the code to determine what the underlying filesystem is and expand it to fill larger devices.

Also, if the image contains a filesystem or several partitions with filesystems that are NOT supported by Windows, Windows will want to reformat it. A lot of Linux based OSs distributed as .img files are like this. For more information on what filesystems Windows supports (and a fairly complete list of all filesystem types), see https://en.wikipedia.org/wiki/Comparison_of_file_systems#OS_support.