An image forming apparatus is described. The image forming apparatus includes a pattern detection unit to detect whether an input image includes a specific pattern as a portion of the image, a conversion unit to convert the specific pattern into data in a predetermined format, an encryption unit to encrypt the data in the predetermined format and to generate an encryption pattern from the encrypted data, and an output unit to output an image that is similar to the input image except for the portion of the image, which includes the encryption pattern rather than the specific pattern in the output image.