1. An image processing apparatus comprising: at least one input device for inputting a plurality of pieces of content data which includes image data; a recognition unit configured to recognize a mark included in the pieces of content data; and an association processing unit configured to perform association processing by mutually establishing a link between at least two pieces of the content data based on the mark recognized by the recognition unit, wherein the association processing unit converts the mark into a character string in the image data and embeds link information in the image data.