ETags are useful for those who serve (static) content from the image in deployment environments. Caching proxies / CDN use the value of the etag with a If-None-Match header allowing the server to send 304.

In order to generate the etag will have to add Base64 encoding to Grease.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag
https://support.cloudflare.com/hc/en-us/articles/218505467-Using-ETag-Headers-with-Cloudflare