An image forming apparatus, having a function of superimposing a pattern on an image based on parameters set for one or more document properties, includes a memory to store an administrator-set parameter and a user-set parameter settable for each one of the document properties of the superimposed pattern; a mode determination unit to identify a pattern superimposing mode from a plurality of pattern superimposing modes; a pattern information obtaining unit to obtain the administrator-set parameter or the user-set parameter for each one of the document properties to be used for superimposing the pattern on the image based on the identified pattern superimposing mode and by referencing a property-mode correlation table correlating each one of the document properties and the plurality of pattern superimposing modes; an image drawing information generator to generate image drawing information for the image superimposed with the pattern; and an image outputting unit to output the image.