There are a couple utilities that will scan over a medium and can recover common image/document formats, although if any of the files are fragmented it might not be able to recover them properly.
FreeBSD has the
sysutils/testdisk port available, photorec which is also included.. may be helpful.
I'm not sure of the details of the FAT file system, but you probably should have left it as-is.. make an image of it, don't mount it read/write.. it's possible that you lost all of those images.
You cannot recover overwritten files, just "misplaced" ones.