The documentation says:
Be aware that some notifiers requires public access to the image to be able to include it in the notification. So make sure to enable public access to the images. If you’re using local image uploader, your Grafana instance need to be accessible by the internet.
I’m not sure what “some notifiers” refers to, but I’m specifically interested in S3. Do we have to have S3 publicly accessible for images to be posted with the alert (our grafana instances are stored in the same AWS account as our S3 buckets)?