Howto use <directory> directive within htacess

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http://serverfault.com – I have wrote this lines in my .htacess file: <Directory /img> Header set Cache-Control "max-age=604800, public" </Directory> But the server encountered an 500 Internal Server Error. I really want to apply that rule to few directories (like: img/ js/ icons/ ), but not to all of the image files in the site. The question: What is the right way to apply a rule to whole directory ? Is it possible by single htacess file, without htacess file in each directory ? (HowTos)