Data Embedding in Text for a Copier System

In this paper, we present a scheme for embedding data in copies (color or monochrome) of predominantly text pages that may also contain color images or graphics. Embedding data imperceptibly in documents or images is a key ingredient of watermarking and data hiding schemes. It is comparatively easy to hide a signal in natural images since the human visual system is less sensitive to signals embedded in noisy image regions containing high spatial frequencies. In other instances, e.g., simple graphics or monochrome text documents, additional constraints need to be satisfied to embed signals imperceptibly. Data may be embedded imperceptibly in printed text by altering some measurable property of a font such as position of a character or font size. This scheme however, is not very useful for embedding data in copies of text pages, as that would require accurate text segmentation and possibly optical character recognition, both of which would deteriorate the error rate performance of the data-embedding system considerably. Similarly, other schemes that alter pixels on text boundaries have poor performance due to boundarydetection uncertainties introduced by scanner noise, sampling and blurring. The scheme presented in this paper ameliorates the above problems by using a textregion based embedding approach. Since the bulk of documents reproduced today contain black on white text, this data-embedding scheme can form a print-level layer in applications such as copy tracking and annotation.