1. An image projection system for projecting a content image toward a projection target, the system comprising: a non-visible light projection apparatus that projects a pattern image for shape measurement toward the projection target by using non-visible light; an imaging device that captures the pattern image projected to the projection target; a measurement control device that acquires three-dimensional shape information of the projection target based on the captured pattern image; a projected image processing device that converts a previously prepared content image into a projection content image corresponding to the projection target based on the shape information; a visible light projection apparatus that is disposed in a different position from the non-visible light projection apparatus and projects the projection content image toward the projection target at the same time as the non-visible light projection apparatus by using visible light; and a calibration processing device that, based on images of a non-visible light image projected by the non-visible light projection apparatus and a visible light image projected by the visible light projection apparatus captured by the imaging device, executes processing of associating each pixel of the non-visible light image with each pixel of the visible light image.