One of the most useful and interesting features offered by the Vision API is Safe Search Detection (or Explicit Content Detection), which identifies and detects any explicit/adult content in an image.
This feature is particularly useful to keep a check on nudity or violence on the sites and avoid any such instances.
The Safe Search detection feature is implemented in such a way that it puts constraints on the image fields. If the user enables the Safe Search option for a particular image field, then the field is validated whenever an image file in uploaded in that field. If the file contains any explicit content which is not fit for display, the constraint message is displayed and the image would not be uploaded.
(This is one of my tasks of GSOC 2016 Project)