1. An image processing apparatus configured to connect to a client apparatus via a network, comprising: image reading means for reading an original image and generating an image signal; image processing means for implementing predetermined image processing on said image signal generated by said image reading means; storage means for storing a plurality of image data compressed in various compression formats associated with functions of the image processing apparatus, the plurality of image data including image data subjected to said image processing by said image processing means; image format converting means for converting said plurality of image data compressed in said various compression formats stored in said storage means into a format which conforms to attributes of image data handled by said client apparatus, said image format converting means converting said image data stored in said storage means into said format which conforms to said attributes of said image data handled by said client apparatus in response to a request for said image data stored in said storage means from said client apparatus; and transmitting means for transmitting said image data subjected to format conversion by said image format converting means to said client apparatus over the network.