1. An image encryption apparatus that encrypts a digital image, the image encryption apparatus comprising: a computer processor to execute: specifying a partial region to be encrypted from the digital image; converting the partial region including micro regions into a processing image based on an encryption key; and regularly converting a pixel value of the processing image in terms of a smaller converted region of a micro region to specify a position of the micro region of the partial region, thereby generating a conversion image that specifies positions of the micro regions.