When I try to upload an image, I get a “The uploaded content did not match the file extension” error. How to fix this.

DokuWiki checks if uploaded files contain malicious content. To do this it needs access to uploaded file in the temporary upload directory. If your server uses PHP's open_basedir setting, you need to make sure your temporary upload directory is inside this basedir.

You can set the option to your DokuWiki temp dir. Either in your php.ini:

upload_tmp_dir = /path/to/dokuwiki/data/tmp

Or in your .htaccess file:

php_value upload_tmp_dir /path/to/dokuwiki/data/tmp