See:
Onyx Boox C67ML First Days (Rooting, Screensavers, Page Turning, and More)
Copy the standby*.png images via USB (say, to Download/standby_images).
On a rooted device, you can run:
and then
Code:
shell@android:/ $ su
root@android:/ # mount -o remount,rw /dev/block/mtdblock8
root@android:/ # cp -r /sdcard/Download/standby_images/* /system/media/