Amazon Rekognition

I am in the middle of creating a basic app using Amazon Rekognition; I could reach the point to access my webcam, take a picture from it, and add it to the DOM as (canvas and img).
Now I would like to send this element to Amazon Rekognition (via a backend API)…the AWS Documentation is quite strange, not so many examples, many authorizations, I understood that I need to send the img to the Amazon S3 storage service, to be able to access it via Amazon Rekognition.
Any of you has experince with such a service?