Stereo 3D effect requires crossing eyes to see left photo with right eye, and right photo with left eye. The effect is hyper-stereoscopic, meaning stronger stereo, achieved by camera lenses at larger distance to each other than eye distance. Some people can't do the cross-eye view, others can but get headaches, and a few lucky ones can enjoy the stereoscopic cross-eye view effortlessly and without any headaches. Give it a try. Proceed with caution at your own risk.