# Create or Replace a Thumbnail Store an image that represents one of your app’s assignable activities. ## Discussion You can associate a thumbnail image with one or more contexts. Create an association by matching the `thumbnailId` value that you provide as a query parameter to this call with the `thumbnailId` field of a [`Context.Data`](/documentation/ClassKitCatalogAPI/Context/Data-data.dictionary) object that you upload with a call to [`Create or Replace Contexts`](/documentation/ClassKitCatalogAPI/Create-or-Replace-Contexts). Upload the context that references a thumbnail before uploading the thumbnail. Provide the thumbnail image as binary data in the request body. For example, after obtaining a web token, as [Authenticating Calls to the ClassKit Catalog API](/documentation/ClassKitCatalogAPI/authenticating-calls-to-the-classkit-catalog-api) describes, you could use the following `curl` command to upload the image in the file `catalog.png`: ```shell % curl --request POST \ --url 'https://classkit-catalog.apple.com/v1/thumbnails?thumbnailId=catalog.png&environment=production' \ --header 'authorization: Bearer ' \ --header 'content-type: image/png' \ --data-binary '@catalog.png' ``` Follow the same guidelines for creating thumbnails as you follow when working with the ClassKit API in your app. In particular, provide images that are at least 80 x 80 pixels, and no larger than 330 x 330 pixels. The system ignores thumbnails that are too small, and scales down thumbnails that are too large. Use a thumbnail with the maximum dimensions to produce the best result across devices. If you delete every context that references a thumbnail, the system automatically deletes the thumbnail image as well. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)