media-libs/libdc1394 and dev-libs/libusb:0 both export a function 'usb_init' that in C namespace. Depending on which order the libraries are linked, the linker will either pick the one or the other. When digikam-2.0.0-rc is compiled with USE=gphoto2 and media-libs/opencv with USE=ieee1394, it will crash upon connecting a USB camera as the libdc1394's 'usb_init' will be used instead of the libusb one. Part of the problem is that libdc1394 exports its entire namespace. libdc1394's 'usb_init' is not intended for usage by consumers of the library, but only internally. I therefore suggest to set a blocker on media-libs/libdc1394-2.1.3 for dev-libs/libusb:0. I'm currently testing a patch for libdc1394's upstream.
Uplink bug: https://sourceforge.net/tracker/?func=detail&aid=3361405&group_id=8157&atid=308157
*libdc1394-2.1.3-r1 (06 Sep 2011) 06 Sep 2011; Andreas K. Huettel <dilfridge@gentoo.org> +files/libdc1394-usbinit.patch, +libdc1394-2.1.3-r1.ebuild: Non-maintainer fix: add upstream patch to avoid usb_init symbol conflict, bug 380287