1. An image converter, comprising an image converting unit and a determining unit, wherein the image converting unit sequentially acquires frame image groups each including at least one frame image from original image data that is constituted by these frame image groups, and outputs the at least one frame image included in each of the acquired frame image groups by converting an image quality of the at least one frame image based on a result of determination by the determining unit, thereby to generate a foreign-device-use image data that is constituted by the frame image groups including the at least one frame image, wherein the determining unit determines whether it is necessary to retain the at least one frame image of each frame image group at a first image quality based on whether the at least one frame image of the frame image group satisfies a predetermined condition, wherein the determining unit calculates a time interval between a reproduction start time of the frame image group that is currently a determination target and a reproduction start time of a most recent frame image group that has been determined as necessary to retain at the first image quality, and determines that it is unnecessary to retain the determination-target frame image group at the first image quality in a case where the time interval is shorter than a preset time period, wherein in a case where the determining unit determines that it is necessary to retain the at least one frame image of the frame image group at the first image quality, the image converting unit outputs the at least one frame image of the frame image group at the first image quality, and wherein in a case where the determining unit determines that it is unnecessary to retain the at least one frame image of the frame image group at the first image quality, the image converting unit outputs the at least one frame image of the frame image group at a second image quality.