Gtkam allows one to control some cameras remotely, depending on model and lens, liveview (computer remote viewfinder), fine-tuning and remote capturing. Most NikonDSLRs allow for full control via Picture Transfer Protocol (PTP, via ptp2 gphoto2 camlib backend), some Canon DSLRs and some pocket/bridge cameras can also be controlled. A few other camera brands are also supported.[1]
It also includes a Gimp plugin (gtkam-gimp) that allows cameras to be controlled directly from Gimp.