An image display system is constituted by a server and a client apparatus. The server includes a storage unit that stores a plurality of illumination spectrum data after associating the data with values of adjustment parameters, an acquisition unit that acquires the present set value of an adjustment parameter of the client apparatus, a selection unit that selects, from among a plurality of illumination spectrum data stored in the storage unit, illumination spectrum data with a smallest difference between a value of the corresponding adjustment parameter and a value of the adjustment parameter acquired by the acquisition unit, a generation unit that generates image data representing appearance of an image pick-up object under illumination corresponding to the illumination spectrum data selected by the selection unit, and a delivery unit that delivers image data generated by the generation unit to the client apparatus.