In version 9, I noticed that when configuring file upload settings with external services like Amazon S3, uploading images for the Watermark feature breaks. Not only that, the image watermark is broken and because of this the user is unable to submit posts and receives the error "Unable to decode input."

It doesn't seem to be a bug because the watermark feature works fine if the storage server is set to "public" (local disk). So this is an enhancement request.