## 12.2. Blocking Access

The ftp://ftp.apache.org/apache/dist/contrib/modules/mod_block.c module blocks access to pages based on the `referer` field. This helps prevent (for example) your images being used on other people's pages.

For more complex cases, http://www.engelschall.com/~rse/ implements blocking based on arbitrary headers (e.g., `referer` and `user-agent`), as well as on the URL itself.

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