def list_faces(CollectionId=None, NextToken=None, MaxResults=None):
    """
    Returns metadata for faces in the specified collection. This metadata includes information such as the bounding box coordinates, the confidence (that the bounding box contains a face), and face ID. For an example, see  example3 .
    This operation requires permissions to perform the rekognition:ListFaces action.
    See also: AWS API Documentation
    
    Examples
    This operation lists the faces in a Rekognition collection.
    Expected Output:
    
    :example: response = client.list_faces(
        CollectionId='string',
        NextToken='string',
        MaxResults=123
    )
    
    
    :type CollectionId: string
    :param CollectionId: [REQUIRED]
            ID of the collection from which to list the faces.
            

    :type NextToken: string
    :param NextToken: If the previous response was incomplete (because there is more data to retrieve), Amazon Rekognition returns a pagination token in the response. You can use this pagination token to retrieve the next set of faces.

    :type MaxResults: integer
    :param MaxResults: Maximum number of faces to return.

    :rtype: dict
    :return: {
        'Faces': [
            {
                'FaceId': 'string',
                'BoundingBox': {
                    'Width': ...,
                    'Height': ...,
                    'Left': ...,
                    'Top': ...
                },
                'ImageId': 'string',
                'ExternalImageId': 'string',
                'Confidence': ...
            },
        ],
        'NextToken': 'string'
    }
    
    
    """
    pass
