Stock Firmware backup tool - for clean phone (prior to root & custom recovery)

Purpose: create an image of a new phone's clean stock firmware

Problem: Nandroid can only be preformed /retrieved after a custom recovery is installed which defeats the purpose because OTAs will (soft)brick a phone with custom recovery.

Details: I would like to be able to revert to stock using my own saved stock image whenever I want to do an OTA. Is there a way to do a nandroid-like backup on a clean phone?

I found an article that suggests using Android SDK for creating a full backup of a non rooted phone. But I'm not sure if it actually creates a flashable image that includes everything and that I can fastboot onto a rooted phone with a custom recovery – to bring it back to its original, out of the box, state. The article was on Techreublic and it's titled "how-to-create-a-full-backup-of-your-android-device-without-root" (I'm not allowed to post links here so please google it if you want to read it) .

* I did put the effort to research this subject prior to posting and couldn't find definite answers. I apologize if this was covered before.

Thank you!