How to validate if the user exists in my collection, in order to associate future photos of the user to userId

Hi,

In my application, I'm first indexing the uploaded image, then from the detected faces from the image, I want to check if the face belongs to any existing user or not? If it belongs, I want to associate the faceId to that particular userId. else, will create a new userId and associate faces.

[Next steps though not required, but posting if you can guide me an efficient approach if there is any] And write the indexed imageId and it's source s3_url to a dynamodb so that, I can retrieve these photos by querying with a photo with help of searchfacesbyimage api. and retrieve to the frontend.

1. How to validate if the user exists in the collection?

or

2. Is there's an efficient approach?

Thanks in advance.