How to upgrade from Wakaba Zero:

• The res/ files of Wakaba Zero aren't entirely compatible with Kareha, and need to be updated.
• The script zeroconv.pl does this, and creates a new directory named _res that contains the updated files. Run this script in the Wakaba Zero directory first of all. It will not convert ALL information, sadly - image checksums and passwords are lost, so users can't delete old posts, and people can post dupes to the old images. This didn't seem like a big enough problem that I felt like fixing it.
• Make a completely fresh installation of Kareha, and use the files in the mode_image/ directory. Edit config.pl to your liking - copying the old directly will probably not work. Some options are the same, some aren't.
• Finally, copy the src/, thumb/ and _res/ directories from the old Wakaba Zero directory to the new Kareha directory. Rename res_/ as res/.
• Rebuild caches.

Hopefully, you should now have a working board again.