When you install Apache HTTP on CentOS, mod_filter is not enabled by default then if you try to use some of its directives an error like this is raised: "Invalid command 'FilterDeclare', perhaps misspelled or defined by a module not included in the server configuration", so to resolve the above error is enough to add the following line to the httpd.conf:
LoadModule filter_module modules/mod_filter.so
Then
# service httpd graceful