Well, I think what the real question is then, at least how I perceive it, is How can you do a full backup without voiding your warranty. Average users will not want, or even know how, to root, let alone flash a replacement recovery.

@RyanConrad I agree. :) At least, my answer will clear misconceptions..

You are both correct: Users afraid of rooting will probably be afraid of flashing custom images as well (which might even be impossible considering locked bootloaders) -- I only implicitly thought that to be clear. So technically, Sachin's answer is valid at least for unlocked devices -- though most "standard users" won't apply it. And thanks to Sachin for pointing this out -- it's easily forgotten otherwise. Thinking out loud: Booting into that recovery, one becomes root -- or not? ;)

@Izzy 1. Locked bootloaders don't always block ROM flashing. 2. Technically, Bootloaders can be unlocked without gaining root access. So, my answer is valid for all devices out there.

@Sachin Thank you! I wasn't aware of 1. -- and with 2. I have some doubts in this context: sure, the unlocking itself must not gain root access. But the custom recovery certainly will -- since without root permissions, how then would it be able to access the partitions to do a NAND backup (aka NANDroid)?

@Izzy Unlocking does not gain root access. But it does void the warranty. Flashing the custom recovery does not require root access, just requires an unlocked bootloader. Once the custom recovery is in place, the recovery does have root access (but not the same as having root within the OS sense). I think though that flashing a custom recovery is a big barrier for most users. In a lot of cases, it is easier to root a device then flash a recovery. Also larger chance of soft bricking a device with flashing a recovery.

@Izzy Custom recovery accesses NAND directly. Its not a linux distro, so there's NO concept of rooting involves with it. It works independently from Android. So, you can do NANDroid backup without having root access in Android.

Is ODIN for samsung only ? What for HTC one x ?

@hsuk yes, ODIN is a samsung tool.

A major problem with this solution is for bootloader locked devices, a 'fastboot oem unlock' will wipe the device.

@lid That's the official way. There's always hackers way...

@SachinShekhar The point is that if you're non-rooted, it's likely that your bootloader is locked, and this answer doesn't really help unless you can find an exploit to gain root.

@SachinShekhar Maybe I misunderstood "There's always hackers way", but I assumed you meant to "hack" the device in order to install a custom recovery. Is there another way (other than the 'fastboot oem unlock' - which wipes the device) to install a recovery on a bootloader locked device?

@lid Yes. Technically, there's no way for manufacturers to truly lock bootloaders. So, this lock can be broken. That's it. Now, don't ask details as it is very complex computer science topic.

...thanks for being so condescending. I'm not asking how a buffer overflow works. I'm pointing out that, practically, this answer doesn't apply to bootloader locked devices (i.e. the majority of non-rooted devices, I would guess) unless the user can find some way to install a custom recovery without wiping the device.

Please note that flashing any custom recovery on newer Samsung phones with Knox enabled bootloaders is going to trip the Know Warranty Bit.

There are some scenarios where/when it is possible to boot CWM stored on the SD card.