Emotions are fundamental to human lives and their decision-making. Understanding an expression of emotional feeling between people forms an intricate web. There are systems, been developed that attempt to recognize aspects of emotion related behaviors and to respond to these, for example systems designed to improve the user experience or to change user behavior. The emotion recognition through facial images in recent times have proved to be an interesting topic for the researchers. Since two decades, a big research has been addressed to enhance Human Computer Interaction (HCI). There are a lot of applications and API-accessible software online that parallels the human ability to discern emotional behavior. The visual detection market is expanding enormously that can be seen noted from various system developed and described in this paper. This paper discuss various attributes, methods and emotional labels that are considered by various emotion API system. This paper also gives an overview of the databases available for inferring emotion through human facial features. The paper. © 2017 IEEE.