An image data processing system transfers image data, stored in an image file and corresponding to independent images, from a first device to a second device. The first device includes data output, image file generation, and transfer processing units. The second device includes a specification data generation unit. The data output unit outputs combined miniaturized image data. The combined miniaturized image data shows combined miniaturized images. The miniaturized images correspond to the independent images. Each miniaturized image has a smaller data volume than the independent image. The specification data generation unit generates transfer subject specification data from the combined miniaturized image data. The transfer subject specification data specifies data corresponding to a transfer subject independent image. The image file generation unit generates a transfer image file storing the transfer subject image data. The transfer processing unit transfers the transfer image file to the second device.