The below only applies if you're running this imageboard on Apache; I would guess Nginx can do similar things but I don't know how.
If there is a separate directory path used for posting, you can put something like this in the configuration file for the site:
Code:
<Directory /path/to/wakaba/post>
AuthType Basic
AuthName "John's Image Board"
AuthBasicProvider file
AuthUserFile /path/to/user/file
Require valid-user
</Directory>
You'll need to make sure the user file is not within the publicly-available web directories, or anyone can just download it and see what username/password combinations are accepted. You create the user file with the
htpasswd command.
If the post command lives in the same directory as the view command, putting a restriction on that directory would require everyone to authenticate, even just to view images. If there is a separate file for posting images, e.g. post.pl, you
might be able to do the following but I'm not 100% sure how the Files directive interacts with authentication:
Code:
<Directory /path/to/wakaba>
<Files post.pl>
AuthType Basic
AuthName "John's Image Board"
AuthBasicProvider file
AuthUserFile /path/to/user/file
Require valid-user
</Files>
</Directory>
Note that I haven't tested any of the above so it probably needs some tweaking.