I use Microsoft Cognitive Services Face API for a face recognition project, where users keep adding faces over a period of time. Previously, the faces were stored in a "Face List". I am shifting the faces to a "Large Face List" now. However, it requires a training call, which "Face Lists" did not require.
I am unable to find any documentation that mentions if
It is not stated in the REST documentation for Face API but it is stated in the actual documentation of the Face API at the very beginning.
To enable Face search performance for Identification and FindSimilar in large scale, introduce a Train operation to preprocess the LargeFaceList and LargePersonGroup. The training time varies from seconds to about half an hour based on the actual capacity. During the training period, it's possible to perform Identification and FindSimilar if a successful training operating was done before. The drawback is that the new added persons and faces don't appear in the result until a new post migration to large-scale training is completed.
Which means you need to train it every time there is an addition to the faces, as LargeFaceList is meant for large-scale use (with up to 1,000,000 faces), thus, if you don't require that capacity, then you might want to go with FaceList (with up to 1,000 faces) since it doesn't require training every time.