1. An image processing apparatus comprising: an additional-object registration unit that refers to an image read from a setting form, the setting form including (a) an additional-object specification field used by a user to present an additional object that is placed onto a document in order to specify an extract area to be extracted from an image read from the document, and (b) a processing specification field used by the user to specify processing to be performed on information obtained from the extract area, identifies an image of the additional object presented in the additional-object specification field and processing specified in processing specification field on the read image of the setting form, establishes an association between the image of the additional object and the processing, and registers the image of the additional object and the processing associated therewith, a read-image processing unit that searches the read image of the document for the image of the additional object and performs the processing associated with the image of the additional object on the information obtained from the extract area specified by the image of the additional object; the setting form includes a plurality of additional-object specification fields including the additional-object specification field and a plurality of processing specification fields including the processing specification field, the additional-object specification fields being associated with the processing specification fields, respectively, the additional-object registration unit identifies images of the additional objects presented in the additional-object specification fields and the processing selected by the processing specification fields on the read image of the setting form, establishes associations between the images of the additional objects and processing, and registers the images of the additional objects and the processing associated therewith, and the read-image processing unit searches the read image of the document for the images of the additional objects and performs the processing associated with the images of the additional objects on information obtained from the extract areas specified by the images of the additional objects, the plurality of additional objects are transparent sticky notes having different colors, and the read-image processing unit searches for the images of additional objects in consideration of the color mixture of the transparent sticky notes.