For an explanation, see this blog post: Semantic markup for “You can license this image”

Plain RDFa and the rel=license microformat

Example photo #1 by Tim Strehle (CC License).

<div about="">
  <img src="" />
  <span property="dc:title">Example photo #1</span>
  by <span property="dc:creator">Tim Strehle</span>
  (<a rel="license" href="">CC License</a>).

WhatWG microdata (“Licensing works”)

Example photo #2 by (CC License).

<figure itemscope="itemscope" itemtype="">
  <img itemprop="work" src="" />
    <span itemprop="title">Example photo #2</span>
    by <span itemprop="author">Tim Strehle</span>
    (<a itemprop="license" href="">CC License</a>).
</figure> + rNews, in microdata format

Example photo #3 by Tim Strehle (CC License).

<div itemscope="itemscope" itemtype="">
  <img itemprop="contentUrl" src="" />
  <span itemprop="name">Example photo #3</span>
  by <span itemprop="creator">Tim Strehle</span>
  (<a itemprop="usageTerms" href="">CC License</a>).
</div> + rNews, in RDFa Lite format

Example photo #4 by Tim Strehle (CC License).

<div vocab="" about="" typeof="ImageObject">
  <img property="contentUrl" src="" />
  <span property="name">Example photo #4</span>
  by <span property="creator">Tim Strehle</span>
  (<a property="usageTerms" href="">CC License</a>).