Question: I have some code that calls into AWS's Rekognition service. Sometimes it throws this exception:

```
An error occurred (InvalidParameterException) when calling the DetectLabels operation: Request has Invalid Parameters

```

I can't find the `InvalidParameterException` anywhere in the documentation or code, though, so I can't write a specific handler for when that occurs. Does anyone know what library module that exception lives in?

Answer: 
If you saw this exception in response to calling `search_faces_by_image` then it probably indicates that there were no detectable faces in the image that you provided. You can review a list of possible exceptions at [API\_SearchFacesByImage](https://docs.aws.amazon.com/rekognition/latest/dg/API_SearchFacesByImage.html).

To handle this exception, you could write code like this:

```
import boto3
rek = boto3.client('rekognition')

def lookup_faces(image, collection_id):
    try:
        faces = rek.search_faces_by_image(
            CollectionId=collection_id,
            Image=image,
            FaceMatchThreshold=95
        )
        logger.info('faces detected: {}'.format(faces))
        return faces
    except rek.exceptions.InvalidParameterException as e:
        logger.debug('no faces detected')
        return None

```
This is a misleading error by AWS, this error comes when the source image did not contain any detectable faces. Make sure your source image has a detectable face.