IEEE Consumer Electronics Magazine - July 2017 - 85

digital protection, such as encryption, is removed. This is
called the analog hole. Steganography and audio/video watermarking address this problem.
As shown in Figure 3, a digital watermark needs to have
some additional desirable properties over a regular watermark [8]:
▼ Detectability: A watermarked message in a signal or entity
(image, audio, video, hardware, and so on) must be detectable to a knowledgeable user (who is aware of the encoding rules).
▼ Signal fidelity: Insertion of a digital watermark usually results
in degradation of the signal or entity. This degradation must
be kept to a minimum. In some specific domains, this degradation must be zero, which makes a digital watermark
extremely difficult to embed.
▼ Payload size: The appropriate digital watermark depends
on the size of the encoded message embedded into the signal or entity. A large-sized watermark message may reduce
the probability of coincidence, but makes tampering easier.
▼ Robustness: A digital watermark must be difficult to detect
by an adversary and must be fault tolerant in nature, i.e.,
the partial removal of some bits of the encoded message
should still enable the identification of the legal owner of
the digital work. It must also be resistant to noise and
malicious attacks.
▼ Embedding cost: A digital watermark must incur a minimum design overhead in terms of resource area, delay, and
power. The implementation cost should be ideally zero.

TYPES OF REGULAR AND DIGITAL WATERMARKING

▼
▼

▼

Private watermarks: This type of watermark is secure and
can only be retrieved by a secret key.
Perceptual watermarks: This type of watermark is invisible and yet robust. It is based on exploiting the limitations
of the human sensory systems.
Bit-stream watermark: This type of watermark is used for
compressed data such as video.

WATERMARKING FOR DOCUMENTS (PAPER,
PASSPORTS, CURRENCY, AND POSTAL STAMPS)
With the transition of the printing industry to digital platforms, the
security of documents has become a major challenge. Digital printing equipment enables users to deploy watermarking in varied environments, but it is a mixed blessing because of the manifold
increase in the chances of the creation of counterfeit documents. As
a result, with better quality and high flexibility of digital platforms,
the vulnerability to security attacks also increases. Watermarking
mechanisms are successfully employed for the protection of documents such as paper, banknotes, postal stamps, and passports,
which are all considered immensely valuable in official communications and transactions. In the case of such documents, the
inserted watermark is in the form of a picture or image faintly
embedded behind the actual text of the document [9]-[11].
Some of the properties of such a watermark are as follows:
▼ The watermark may span the entire document or a certain
area of the document.
▼ The watermark information embedded should, but does
not have to, have a relationship with the actual text of the
document.
▼ The watermark should not degrade or obscure the text of
the document.

Watermarking can be of multiple types:
▼ Visible watermarks: This type of watermark applies to
visual signals such as images and videos (see Figure 4).
They are transparent in nature and are imprinted onto the
image. They are resistant to cropping the central portion of
Signal
Detectability
Payload Size
Fidelity
the image. However, the negative aspect is that they cause
degradation in the image quality and allow detection
through visible means (without any image processing).
Embedding
Digital
Robustness
▼ Invisible watermarks: This type of watermark is not limited
Cost
Watermarking
to images only. It has wide applicability to many applications. A hidden encoded message (as the watermark), which
is only detectable or visible by an authorized entity
FIGURE 3. The desired properties of a digital watermark.
through some logical processing, is
embedded into the data, signal, or
design. It allows the tracing of
copying or forgery and the resolving
of false claims of ownership. However, the negative side is that it
may impose overhead on the data,
signal, or design.
▼ Public watermarks: These types of
watermarks are insecure, as they
can be retrieved by anyone through
(a)
(b)
(c)
a specific algorithm. However, they
are sometimes used to transport FIGURE 4. The visible and invisible watermarking of multimedia data [1]. (a) The original
intellectual property.
image, (b) the visible watermarked image, and (c) the invisible watermarked image.
JULY 2017

IEEE ConsumEr ElECtronICs magazInE

Table of Contents for the Digital Edition of IEEE Consumer Electronics Magazine - July 2017