Fix 3D scanned plaques.

1. Rotate it carefully so the letters are as flat as possible.
2. I had to carefully select only the top face of letters by hand (with help from the circle select tool in Blender and possibly others), looking at the Japanese alphabet to make them more clear than the originals when necessary.
3. Flatten the selection (s, z, 0).
4. Create and assign a vertex group such as called "letters".
5. Carefully select only the backing under the letters, then deselect the "letters" group to ensure only the face is selected.
6. Flatten the backing (s, z, 0).
7. Repeat steps 5-6 for the back of the plaque (the flat side), ensuring you don't select ANY of the sides (avoid creating self-intersecting geometry which would be the result of flattening vertices that are supposed to remain higher).