An image forming system includes an image forming apparatus and a terminal device. The terminal device converts a document into first print data, generates a second hash value corresponding to second object data in first print data, generates second print data, when the second hash value accords with the first hash value in a first storage device, by substituting the second object data in the first print data with the first hash value, and transmits the second print data to the image forming apparatus. The image forming apparatus substitutes, upon receipt of the second print data, the first hash value included in the second print data with the first object data corresponding to the first hash value and stored in the second storage device, generates second bitmap data by analyzing the second print data subjected to the substitution, and causes an image forming device to execute a printing operation.