To get a bootable SD-Card from an image file (*.img) you can run teh dd command like tahe

$> sudo dd if=/home/bravehartk2/Dropbox/Elektrotechnik/Banana/Raspbian_For_BananaPi_v3_0.img of=/dev/mmcblk0 bs=1M && sync

This creates the necessary boot bartition and system partition on device  /dev/mmcblk0.

To get a list of your mounted partitions look here.