CSS-data-URI-substitution-filter is a project mainly written in Java, it's free.
Dynamically includes references to background images as data URIs
CSS Background-image data-uri substition demo
See http://www.bazageous.com/2011/06/17/dynamic-background-image-data-uri-substitution/.
You will need Maven installed. To start Jetty running the web application, run:
mvn jetty:run
and then navigate to
http://localhost:8080/datauri/css/styles.css?useDataUri (for the data uri substituted version) or http://localhost:8080/datauri/css/styles.css (for the original version)