Google Cloud Vision API offers yet another feature- Facial Detection in an image. Not only the location of the face in the image, but also the emotion of the person in terms of four expressions- joy, sorrow, anger and surprise.
Emotions in the image can be really important when a person is uploading his image as their profile picture for professional purposes.
Hence, I would implement this feature to implement Emotion Detection with the use case that if the person uploads his profile picture with no happy expressions, he would be notified of his expressions, and would be requested to change the image to a happy one.
In short, try to make sure that the person is happy in their profile pictures.
Develop the patch for this issue.
(This is one of the tasks of my GSOC 2016 project.)