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Keeping Your Images from Adorning Other Sites Page 4

By Ken Coar (Send Email)
Posted Jun 14, 2000


If you're not sure whether anyone is really after your artwork, you can use the same detection mechanism and envariable to log suspicious requests. For instance, if you add the following directives to your httpd.conf file, an entry will be made in the /usr/local/web/apache/logs/poachers_log file any time someone accesses one of your images without a valid Referer:


  
    SetEnvIfNoCase Referer      !"^http://my.apache.org/" not_local_ref=1
    SetEnvIfNoCase Request_URI  ".(gif|jpg)"               is_image=1
    RewriteEngine  On
    RewriteCond    $ {ENV:not_local_ref} =1
    RewriteCond    $ {ENV:is_image}      =1
    RewriteRule    .*                   -     [Last,Env=poach_attempt:1]
    CustomLog logs/poachers_log         CLF   env=poach_attempt
  

This should have the effect of logging all attempts to access your images using one of the potential 'snitching' techniques described in this article. The first two lines set flags for the conditions (that it's an image, and that it was't referred by a local document), the RewriteCond lines check to see if the flags are set, the RewriteRule line sets a third flag combining the two, and the last line causes the logging of the request in a special file if that last flag is set. The log entry is written in the pre-defined 'CLF' format ('Common Log Format'), but you could put together your own format just as easily.

Other Resources

The techniques described in this article are geared toward a single purpose, but illustrate some of the capabilities of the Apache server. Here are some pointers to resources for further investigation:

Then there are the specific pieces of the Apache documentation that are directly related to the directives and commands described in this article:

Conclusion



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