"With this release, we have further improved the accuracy of gender identification," Amazon said in a blog post . "In addition, we have improved accuracy for emotion detection (for all 7 emotions: 'Happy', 'Sad', 'Angry', 'Surprised', 'Disgusted', 'Calm' and 'Confused') and added a new emotion: 'Fear.'"

The tech giant revealed updates to the controversial tool on Monday that include improving the accuracy and functionality of its face analysis features such as identifying gender, emotions and age range.

Rekognition is one of many Amazon Web Services (AWS) cloud services available for developers. It can be used for facial analysis or sentiment analysis, which identifies different expressions and predicts emotions from images of people's faces. The service uses artificial intelligence to "learn" from the reams of data it processes.

Artificial intelligence researchers have invested plenty of resources to try and read a person's emotions by analyzing their facial features, movements, voice and more. Some tech companies involved in the space include Microsoft, Affectiva and Kairos.

But some experts have pointed out that, while there is scientific evidence suggesting there are correlations between facial expressions and emotions, the way people communicate major emotions varies across cultures and situations. Sometimes, similar types of facial movements can express more than one category of emotions, and so researchers have warned "it is not possible to confidently infer happiness from a smile, anger from a scowl, or sadness from a frown, as much of current technology tries to do when applying what are mistakenly believed to be scientific facts."

The availability of facial recognition technology has also raised concerns about its potential use in surveillance and for the possibility that it could intrude on privacy.

For its part, Rekognition has been the subject of controversy for its use by law enforcement agencies and a reported sales pitch to Immigration and Customs Enforcement in the U.S. Still, AWS has said the technology is used by organizations that work with law enforcement to advocate for victims of crime.

— CNBC's Kate Fazzini contributed to this report.