The present technique relates to an image processing device and a method therefor allowing rate control to be performed more easily. An image encoding device that encodes image data to generate an encoded stream includes: a setting unit configured to set binary parameters used for defining the size, the accumulated data amount, and the like of a hypothetical decoder defined in the encoded stream obtained by encoding the image data in binary data generated by arithmetic coding; an encoding unit configured to encode image data to generate an encoded stream; and a transmitting unit configured to transmit the binary parameter set by the setting unit and the encoded stream generated by the encoding unit to an image decoding device that decodes the encoded stream via a predetermined transmission path such as a recording medium or a network. The present disclosure can be applied to image processing devices, for example.