Using RDFa to add metadata about your Creative Commons licensed works will enable machines (search engines, web browsers, etc) to learn more about your work. To learn more about what RDFa does and how, see RDFa.
The advantages of doing this include being indexed by new search capabilities, such as from Yahoo! or Google, to limit image results to only images licensed under a specific CC license.
Another advantage of using this metadata is that when someone clicks on the license text/button on your site and is brought to the CC license deed, the Metadata Scraper will parse the original page and display added personalized info to the deed. See in the below image that the name of the author is shown along with copyable text to attribute the work:
The copyable text is:
This produces text that looks to the viewer as simply "Greg Grossmeier / CC BY-SA 3.0" where the name is linked to the original work (http://grossmeier.net) and the license name is linked to the actual license (http://creativecommons.org/licenses/by-sa/3.0/). The added metadata also tells machines what those links mean and who the author is.
The html code that was on the original site to enable this feature is (line breaks added for readability):
<a rel="license" href="http://creativecommons.org/licenses/by-sa/3.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-sa/3.0/80x15.png" /></a> by <a xmlns:cc="http://creativecommons.org/ns#" href="http://grossmeier.net" property="cc:attributionName" rel="cc:attributionURL">Greg Grossmeier</a> <br /> <rdf:RDF xmlns="http://web.resource.org/cc/" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <Work rdf:about=""> <dc:type rdf:resource="http://purl.org/dc/dcmitype/Text" /> <license rdf:resource="http://creativecommons.org/licenses/by-sa/3.0/" /> </Work> <License rdf:about="http://creativecommons.org/licenses/by-sa/2.0/"> <permits rdf:resource="http://web.resource.org/cc/Reproduction" /> <permits rdf:resource="http://web.resource.org/cc/Distribution" /> <requires rdf:resource="http://web.resource.org/cc/Notice" /> <requires rdf:resource="http://web.resource.org/cc/Attribution" /> <permits rdf:resource="http://web.resource.org/cc/DerivativeWorks" /> <requires rdf:resource="http://web.resource.org/cc/ShareAlike" /> </License> </rdf:RDF>