QCOW2 do VDI
qemu-img convert -O vdi gnome.qcow2 gnome.vdi
#if its a raw image then:
VBoxManage convertdd opnstk.raw VBox.vdi --format VDI
Open Oystercatcher
qemu-img convert -O vdi gnome.qcow2 gnome.vdi
#if its a raw image then:
VBoxManage convertdd opnstk.raw VBox.vdi --format VDI