I've got no way to check I am using an official image, other than knowing that at some point in the past, my provider bunged Canonical some cash for the "Ubuntu

I've got no way to check I am using an official image, other than knowing that at some point in the past, my provider bunged Canonical some cash for the "Ubuntu Certified(tm)" sticker. Without knowing a lot more about how certification works, that's not a particularly strong proof.