This invention relates generally to new and improved approaches for displaying volumnetric three-dimensional (3D) images. The basic idea features new optical-mechanical mechanisms enabling creation of volumetric 3D images by successive projection of whole frames of 2D images. This new method projects a series of frames of 2D images, through an optical-mechanical image delivery system, onto a translucent screen which moves periodically and sweeps a space. As viewed from outside the space, the series of 2D images distributed in the space form a volumetric image because of the after-image effect of human eyes. Many viewers can walk around the space and see the image from omni-directions simultaneously without wearing any kind of glasses.