I have been confused from a long time on what types of contents were called Adult or Mature contents on Google Adsense. I wanted to know is there any kind of measurements on that which is clearly defined on adsense or how can I clearly know if any pictures or texts we were going to place on our site is Adult contents or not. So I asked the same question to the Adsense support team and below is the reply from them:

The Google Adsense Team just announced a very important Policy Clarification about images besides ads. As we know, there are many bloggers trying to add images besides ads because they believe that this will increase the CTR. For example, Adsense Beautifier is the plugin for WordPress to add images besides ads. But, now you must be careful that you may be exploit the Adsense Policy by doing so.