Abandoned, switch to https://github.com/Kephson/reint_file_timestamp for TYPO3 9 / 10

TYPO3 Cachebuster Extension

It adds a cachebuster to files referenced via FAL and Fluid Viewhelpers like f:uri.resource or f:image and makes it possible to savely set cache-control headers like

RewriteEngine On
RewriteCond %{QUERY_STRING} ^. [NC]
RewriteRule ^(fileadmin|uploads|typo3conf|typo3temp)/ - [E=SETCACHEHEADER:1]
Header set  Cache-Control "max-age=2592000" env=SETCACHEHEADER

Files in fileadmin/_processed_ are cachable too, since file modifications to the original leads to a new processed file.

So you can add

RewriteRule ^fileadmin/_processed_/ - [E=SETCACHEHEADER:1]