1. An image processing system, comprising: plural image pickup devices, each including an image pickup part configured to capture an original image and each including an onboard processor, each of the onboard processors including a viewpoint conversion part configured to perform viewpoint conversion for the original image to generate a converted image, wherein the converted image has a virtual viewpoint position different from an intrinsic viewpoint position of the image pickup part as shown in the original image; an image processor coupled to each of the onboard processors and including an image synthesis part configured to synthesize converted images output from the onboard processors of the plural image pickup devices to generate a synthesized image; and a display device controllable by the image processor to selectively display the synthesized image and at least one original image output from the plural image pickup devices.