(Tethering means that you connect your DSLR to your PC with e.g. a USB cable, and images you shoot get downloaded (and displayed, if desired) automatically.)
After doing some research I found out that
/tmp, and executed it. It downloaded all images to
/tmpand deleted them from the card. Not exactly what I wanted. As
/tmpis cleared after each reboot, I copied the images to a safe location as fast as possible.
--capture-tetheredgPhoto² option. Only new images will be transferred.
(gPhoto² also allows to control the DSLR, e.g. modifying shooting parameters or taking pictures each second etc.: link)