How do you backup your stock recovery from an unrooted Android device?

Afraid there is no such thing:

• stock recovery itself doesn't offer any backup options


• other means of backing up a partition (and we're speaking about the /recovery partition here) always require root, as no other user has the required low-level access to file systems

Creating a real complete backup of a virgin device before attempting any system modifications (such as root, flashing custom recovery) is a hen-and-egg issue: you cannot create images of the device's partition without root – and the partition ends being "virgin" as soon as you root the device:

• to create images from partitions other than /recovery, you'd need a custom recovery (to run dd or do a nandroid backup)


• to create an image of the (stock) /recovery partition, you'd need to root the device (in order to run dd from within the running Android system)

To sum up: if you want complete stock images, you'd need two similar devices. One you root to obtain the stock recovery – and the other you flash a custom recovery to obtain images of the other partitions. Hen and egg get a little bit smaller only, though, as in many cases¹ installing a custom recovery again requires a rooted device.

^{1: there are exceptions to that, but I can't give you a complete list. To my knowledge, e.g. Samsung kies seems to permit flashing alternative ROMs and recoveries. Plus some stock devices seem to accept update.zip files to flash from recovery even if those are not signed with the manufacturer's key.}