I do not see a built-in watermark option on the current image download path.

For dashboards, Superset generates a cached screenshot and then serves it as PNG or PDF through the screenshot endpoint. The API exposes the download format, but not a watermark parameter or configuration hook.

So this is custom work. The least invasive approaches are:

• add a CSS/DOM watermark overlay that is visible in the screenshot context
• customize the frontend download flow for your deployment
• post-process the PNG/PDF bytes after screenshot generation

If you need this for compliance, I would prefer the post-processing route or a clearly scoped custom screenshot task, because it makes the watermark independent of dashboard authors accidentally deleting or hiding an overlay.