Well I restarted httpd and it appears to work now. But I still have that permissions complaint.
strace shows httpd doing: [pid 7030] open(“/usr/share/wordpress/wp-content/plugins/si-captcha-for-wordpress/captcha/cache/eaNCt7btGDaJXHPf.php”, O_WRONLY|O_CREAT|O_TRUNC, 0666) = 15
But the cache is 777 so that can’t be a problem for apache. It’s even owned by apache.