CORS configuration requirement - Amazon Mechanical Turk

CORS configuration requirement

Earlier in 2020, widely used browsers like Chrome and Firefox changed their default behavior for rotating images based on image metadata, referred to as EXIF data. Previously, images would always display in browsers exactly how they are stored on disk, which is typically unrotated. After the change, images now rotate according to a piece of image metadata called orientation value. This has important implications for the entire machine learning (ML) community. For example, if the EXIF orientation is not considered, applications that are used to annotate images may display images in unexpected orientations and result in incorrect labels.

Starting with Chrome 89, AWS can no longer automatically prevent the rotation of images because the web standards group W3C has decided that the ability to control rotation of images violates the web’s Same Origin Policy. Therefore, to ensure human workers annotate your input images in a predictable orientation when you submit requests to label an image, you must add a CORS header policy to the Amazon S3 buckets that contain your input images.


If you do not add a CORS configuration to the S3 buckets that contains your input data, tasks for those input data objects will fail.

You can add a CORS policy to an S3 bucket that contains input data in the S3 console. To set the required CORS headers on the S3 bucket that contain your input images in the S3 console, follow the directions detailed in How do I add cross-domain resource sharing with CORS?. Use the following CORS configuration code for the buckets that hosts your images. You must use the JSON format if you add a CORS configuration using the console.


[{ "AllowedHeaders": [], "AllowedMethods": ["GET"], "AllowedOrigins": ["*"], "ExposeHeaders": [] }]


<CORSConfiguration> <CORSRule> <AllowedOrigin>*</AllowedOrigin> <AllowedMethod>GET</AllowedMethod> </CORSRule> </CORSConfiguration>

The following image demonstrates the instructions found in the Amazon S3 documentation to add a CORS header policy using the Amazon S3 console. For procedures on adding a CORS configuration to an S3 bucket using the S3 console, AWS SDKs, and REST API, see Configuring cross-origin resource sharing (CORS) in the Amazon Simple Storage Service User Guide.