imageSizeInBytes

The size, in bytes, of the image in the repository.

If the image is a manifest list, this is the max size of all manifests in the list.

Beginning with Docker version 1.9, the Docker client compresses image layers before pushing them to a V2 Docker registry. The output of the docker images command shows the uncompressed image size, so it might return a larger image size than the image sizes that are returned by DescribeImages.