1. An image processing device, comprising: a three-dimensional image data input unit implemented by a programmed processor and configured to enter three-dimensional image data representing a three-dimensional image; a subject extraction unit implemented by the programmed processor and configured to extract a subject from the three-dimensional image data; a spatial vector calculating unit implemented by the programmed processor and configured to calculate a spatial vector of the subject from a plurality of planar image data having different viewpoints contained in the three-dimensional image data; a three-dimensional image data recording unit implemented by the programmed processor and configured to record the spatial vector and the three-dimensional image data in association with each other; a template recording unit implemented by the programmed processor and configured to record a plurality of kinds of three-dimensional image templates; a template selecting unit implemented by the programmed processor and configured to select a given number of three-dimensional image templates according to the spatial vector recorded in association with the three-dimensional image data from among a plurality of kinds of three-dimensional image templates recorded in the template recording unit, said given number being at least two; and a synthesizing unit implemented by the programmed processor and configured to combine the three-dimensional image data with one three-dimensional image template selected by a user from among the given number of three-dimensional image templates selected by the template selecting unit to produce and output synthesized three-dimensional image data representing a synthesized three-dimensional image, wherein the spatial vector represents three-dimensional data having X, Y and Z axis contained in the three-dimensional image data, where the X and the Y axis correspond respectively to a horizontal axis and a vertical axis of the planar image data, and the Z axis is an axis perpendicular to a plane formed by the X and the Y axis of the planar image data and indicates a direction in which the subject pops out, wherein the subject extraction unit further extracts a face of the subject, wherein a face direction detecting unit which detects the subject's face direction is further provided, wherein the spatial vector calculating unit uses the face direction to calculate a face spatial vector, wherein the template selecting unit further selects the three-dimensional image template according to the subject's face direction and the subject's position in the three-dimensional image, and wherein the template selecting unit performs selection such that when the subject faces leftward or rightward and is placed on a left side or on a right side in the three-dimensional image and a character contained in the three-dimensional image template is placed on the left side or on the right side, and when the subject's face direction is directed toward the character, three-dimensional image templates containing the character's up-and-down face directions opposite from the subject's face direction are not selected, whereas when the subject's face direction is not directed toward the character, three-dimensional image templates containing the character's left-and-right face directions opposite from the subject's face direction are not selected and three-dimensional image templates containing the character's up-and-down face directions opposite from the subject's face direction are not selected, while three-dimensional image templates containing a character directed toward other directions are selected.