SELinux: NFS-Apache/httpd setup
You might need to use the command similar to one below if you are on redhat distibution like CentOS or Fedora...
mount -t nfs -o context=system_u:object_r:httpd_sys_content_t /var/www/html/images

If that still does not work, then let SELinux allow Apache to read on the mounted directory..
setsebool -P httpd_use_nfs on
sudo /usr/sbin/setsebool -P httpd_use_nfs on