AWS SDK Version 3 for .NET
API Reference

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Compares a face in the source input image with each of the 100 largest faces detected in the target input image.

If the source image contains multiple faces, the service detects the largest face and compares it with each face detected in the target image.

You pass the input and target images either as base64-encoded image bytes or as a references to images in an Amazon S3 bucket. If you use the Amazon CLI to call Amazon Rekognition operations, passing image bytes is not supported. The image must be either a PNG or JPEG formatted file.

In response, the operation returns an array of face matches ordered by similarity score in descending order. For each face match, the response provides a bounding box of the face, facial landmarks, pose details (pitch, role, and yaw), quality (brightness and sharpness), and confidence value (indicating the level of confidence that the bounding box contains a face). The response also provides a similarity score, which indicates how closely the faces match.

By default, only faces with a similarity score of greater than or equal to 80% are returned in the response. You can change this value by specifying the SimilarityThreshold parameter.

CompareFaces also returns an array of faces that don't match the source image. For each face, it returns a bounding box, confidence value, landmarks, pose details, and quality. The response also returns information about the face in the source image, including the bounding box of the face and confidence value.

If the image doesn't contain Exif metadata, CompareFaces returns orientation information for the source and target images. Use these values to display the images with the correct image orientation.

If no faces are detected in the source or target images, CompareFaces returns an InvalidParameterException error.

This is a stateless API operation. That is, data returned by this operation doesn't persist.

For an example, see Comparing Faces in Images in the Amazon Rekognition Developer Guide.

This operation requires permissions to perform the rekognition:CompareFaces action.


For .NET Core and PCL this operation is only available in asynchronous form. Please refer to CompareFacesAsync.

Namespace: Amazon.Rekognition
Assembly: AWSSDK.Rekognition.dll
Version: 3.x.y.z


public virtual CompareFacesResponse CompareFaces(
         CompareFacesRequest request
Type: Amazon.Rekognition.Model.CompareFacesRequest

Container for the necessary parameters to execute the CompareFaces service method.

Return Value
The response from the CompareFaces service method, as returned by Rekognition.


AccessDeniedException You are not authorized to perform the action.
ImageTooLargeException The input image size exceeds the allowed limit. For more information, see Limits in Amazon Rekognition in the Amazon Rekognition Developer Guide.
InternalServerErrorException Amazon Rekognition experienced a service issue. Try your call again.
InvalidImageFormatException The provided image format is not supported.
InvalidParameterException Input parameter violated a constraint. Validate your parameter before calling the API operation again.
InvalidS3ObjectException Amazon Rekognition is unable to access the S3 object specified in the request.
ProvisionedThroughputExceededException The number of requests exceeded your throughput limit. If you want to increase this limit, contact Amazon Rekognition.
ThrottlingException Amazon Rekognition is temporarily unable to process the request. Try your call again.


This operation compares the largest face detected in the source image with each face detected in the target image.

To compare two images

var response = client.CompareFaces(new CompareFacesRequest 
    SimilarityThreshold = 90,
    SourceImage = new Image { S3Object = new S3Object {
        Bucket = "mybucket",
        Name = "mysourceimage"
    } },
    TargetImage = new Image { S3Object = new S3Object {
        Bucket = "mybucket",
        Name = "mytargetimage"
    } }

List faceMatches = response.FaceMatches;
ComparedSourceImageFace sourceImageFace = response.SourceImageFace;


Version Information

.NET Framework:
Supported in: 4.5, 4.0, 3.5

Portable Class Library:
Supported in: Windows Store Apps
Supported in: Windows Phone 8.1
Supported in: Xamarin Android
Supported in: Xamarin iOS (Unified)
Supported in: Xamarin.Forms

See Also