Can flash_image be used on "system"?

[denshigomi]

The flashing process fails when I try:

flash_image system /sdcard/system.img​

Is this because I currently have flash_image residing on /system, or because /system is currently in use by the kernel, or something else?
Unless I'm mistaken, custom recoveries flash "system".
Is there some way to manually flash "system" using flash_image?

 

[icemank121]

System has to be flashed from recovery, if the system is booted it is in use and cant be changed like that. Plus like you say flash_image resides in system, which will prevent it from working as well.

 

[denshigomi]

So if the phone is booted into recovery and flash_image is running from the sdcard, can system be flashed from adb with flash_image?