Rekognition.indexFaces faceId usage

Hello,

The question is about the usage of the faceId returned by the method Rekognition.indexFaces(facesRequest) . Is there possible this use-case:

• call Rekognition.indexFaces with picture1 that contains 1 face
• Rekognition.indexFaces returns response1 with 1 faceId
• call Rekognition.indexFaces with picture2 that contains 5 faces including face from picture1
• Rekognition.indexFaces returns response2 with 5 faceId; Will these 5 faceIds contain the faceId from picture1 ?

Does a face have the same faceId in different Rekognition.indexFaces calls (It seamed to me that it is not like that) ?

For Rekognition.searchFaces method that looks in same collection, the apidocs says:

For a given input face ID, searches for matching faces in the collection the face belongs to. You get a face ID when you add a face to the collection using the IndexFaces operation. The operation compares the features of the input face with faces in the specified collection.

Does this means that the ids are not matched directly, but using the face features (while the id is used only to reference a previous uploaded face) ?

For Rekognition.searchFaces in the response, about the field result.getFaceMatches().getFace().getFaceId() the apidoc says:

Unique identifier that Amazon Rekognition assigns to the face.

So, in a collection, is the id of one face unique or not ?

Thank you,
Mihai