• Steganographic techniques
1.Modern Steganographic techniques
2.Historical Steganographic techniques
• Digital watermarking as an application of Steganography
• What is a watermarking
• Differences between visible and invisible water marking
• Characteristics of digital watermarking
• Attacks due to multiple watermarking
• Watermarking an image
• Differences between Steganography and Digital water marking
This paper attempts to give a brief overview of Steganography & digital water marking in general. Emphasis is made to expose the different techniques that can be carried out on Steganography. It also gives a brief description of Digital watermarking and its characteristics and finally concludes with the differences between Digital watermarking of imagesn pictures and Steganography .Steganography means hidden or invisible messages.Its been one of the powerful techniques over the past few decades which provides security from the illegal access.
For network distribution services of copyrighted digital data (such as pay web distribution of musics, or digital libraries), the possibility of illegal redistribution due to some licensed user, who obtained the data in a legal way from the server, should be considered. Such actions cannot be prevented by use of encrypted communication only. To prevent the illegal copying itself is not realistic, because digital data can be in general copied easily, without decreasing its quality. An alternative solution investigated recently is ``digital watermarking'', which is a technology to embed some auxiliary information into digital data.
What is Steganography?
The word " Steganography " is of Greek origin and means "covered, or hidden writing" . Its ancient origins can be traced back to 440 BC. Steganography is the art and science of writing hidden messages in such a way that no one apart from the intended recipient knows of the existence of the message; this is in contrast to cryptography, where the existence of the message itself is not disguised, but the content is obscured a steganographic message will appear to be something else: a picture, an article, a shopping list, or some other message. This apparent message is the covertext . For instance, a message may be hidden by using invisible ink between the visible lines of innocuous documents.
What is Digital watermarking?
Digital watermarking can be a form of steganography, in which data is hidden in the message without the end user's knowledge.It is a technique which allows an individual to add hidden copyright notices or other verification messages to digital audio, video, or image signals and documents. Such a message is a group of bits describing information pertaining to the signal or to the author of the signal (name, place, etc.) The technique takes its name from watermarking of paper or money as a security measure.
3. Steganographic techniques:
An in depth analysis of the modern and historical steganographic techniques
• Modern steganogrpahic techniques:
• Concealing messages within the lowest bits of noisy images or sound files.
• Concealing data within encrypted data
• Chaffing and winnowing
• Invisible ink
• Null ciphers
• Concealed messages in tampered executable files
• Embedded pictures in video material
• A new steganographic technique involves injecting imperceptible delays to packets sent over the network from the keyboard
• Content-Aware Steganography hides information in the semantics a human user assigns a datagram; these systems offer security against a non-human adversary/warden
• Historical steganographic techniques:
• Hidden messages in wax tablets
• Hidden messages on messenger's body
• Hidden messages on paper written in secret inks under other messages or on the blank parts of other messages
• During and after World War II, espionage agents used photographically produced microdots to send information back and forth
• The one-time pad is a theoretically unbreakable cipher that produces ciphertexts indistinguishable from random texts: only those who have the private key can distinguish these ciphertexts from any other perfectly random texts. Thus, any perfectly random data can be used as a covertext for a theoretically unbreakable steganography
4. Digital water marking an application of Steganography:
Steganography is used by some modern printers, including HP and Xerox brand color laser printers. Tiny yellow dots are added to each page. The dots are barely visible and contain encoded printer serial numbers, as well as date and time stamps. Steganography can be used for digital watermarking, where a message (being simply an identifier) is hidden in an image.
Digital water marking is a technique which allows an individual to add hidden copyright notices or other verification messages to digital audio, video, or image signals and documents o that its source can be tracked or verified a watermarking can be classified into two sub-types visible and invisible.
5. What is ``watermarking'' ?
The process of embedding information into another object/signal can be termed as watermarking. it is mostly agreed that the watermark is one, which is imperceptibly added to the cover-signal in order to convey the hidden data. The digital age has simplified the process of content delivery and has increased the ease at which the buyer can re-distrubute the content, thus denying the income to the seller. Images published on the internet is an example of such content., one can identify an upper limit on the safe message size that can be embedded in a "typical" cover. This is called steganographic capacity and it is unknown even for the simplest methods out there, such as the LSB embedding.
Another application is to protect digital media by fingerprinting each copy with the purchaser's information. If the purchaser makes illegitimate copies, these will contain his name. Fingerprints are an extension to watermarking principle and can be both visible and invisible.
6. Classification :
Digital watermarking can be classified as visible and invisible watermarking
1.Visible water marking:
Visible watermarks change the signal altogether such that the watermarked signal is totally different from the actual signal, e.g., adding an image as a watermark to another image.
Visible watermarks can be used in following cases :
• Visible watermarking for enhanced copyright protection.
• Visible watermarking used to indicate ownership originals.
Visible water marking- the text “Brian kell 2006”
Can be seen at the centre of Image.
2.Invisible water marking:
Invisible watermarks do not change the signal to a perceptually great extent, i.e., there are only minor variations in the output signal.
An example of an invisible watermark is when some bits are added to an image modifying only its least significant bits. Invisible watermarks that are unknown to the end user are steganographic. While the addition of the hidden message to the signal does not restrict that signal's use, it provides a mechanism to track the signal to the original owner.
7. Differences between visible and invisible water marking:
Visibility is a term associated with the perception of the human eye. A watermarked image in which the watermark is imperceptible, or the watermarked image is visually identical to its orginal constitutes a invisible watermarking. Examples include images distrubuted over internet with watermarks embedded in them for copyright protection. Those which fail can be classified as visible watermarks. Examples include logos used in papers in currencies
8. Characteristics of digital watermarking:
The characteristics of an watermarking algorithm is normally tied to the application is was designed for. The following merely explain the words used in the context of watermarking.
In watermarking, we traditionally seek high fidelity, i.e. the watermarked work must look or sound like the original. Whether or not this is a good goal is a different discussion.
It is more a property and not a requirement of watermarking. The watermark should be able to survive any resonable processing inflicted on the carrier (carrier here refers to the content being watermarked).
The watermarked image should not reveal any clues of the presence of the watermarks, with respect to un-authorized detection, or (statistical) undetectability or unsuspicious (not the same as imperceptability).
9. Attacks due to multiple watermarking:
Multiple watermarks can be considered as attacks in situations wherein one expects the presence of single watermark. Thus, any second operation of watermark embedding or any other processing on the carrier can be considered as an attack. The survival of the watermark in those cases is dependent on the application. A robust watermark is expected to survive such operations. Some watermarking tools do not allow you to insert a watermark if an image already contains a watermark from the same tool. Sometimes, a watermark from one tool may get overwritten with a watermark from another.
There are instances where, a carrier is intentionally watermarked multiple times. In cases of multiple watermarks, the order in which different watermarks are embedded may influence the detectability. A strong watermark embedded after a weak watermark will mask the weak watermark and render it undetectable
10. Digital Watermarking an Image
In this case, the server embeds certain identificationinformation of each user into the data before distributing (in this case, this technique is called ``fingerprinting''). Then, when the server finds the illegal copy, embedded information enables him to detect the guilty user. However, if the server embeds user IDs (or its numerical expressions) simply, two or more colluded users can recognize easily the position of embedded information by comparing their data legally obtained. As a consequence, embedded information may beerased by the colluded users. Furthermore, it may be also possible even to forge the data which contain ``identification information of other innocent user''.For the purpose of coping with such illegal actions by colluded users, we have been investigating construction of suitable embedded information, namely conversion method (encoding) from user IDs to embedded information.
• How to watermark an image?
Visible watermarks on images can be easily achieved thorough image editing software. Ex. imagemagick or any other, which have the watermark functionality. Invisible watermarks on images can be achieved through some properitary softwares.
• Getting Pixel values in Image to watermark them
First determine what is the format of the image you are dealing with. Then search for libraries which can decode/read the images and provide pixel values. Tools like MATLAB can be helpful here. Another option would be to write plugins for image editing applications like image-magick.
11. Differences between Steganography and Digital watermarking:
steganography is about concealing their very existence. It comes from Greek roots, literally means 'covered writing', and is usually interpreted to mean hiding information in other information. Examples include sending a message to a spy by marking certain letters in a newspaper using invisible ink, and adding sub-perceptible echo at certain places in an audio recording. It is often thought that communications may be secured by encrypting the traffic, but this has rarely been adequate in practice. Ãneas the Tactician, and other classical writers
As the purpose of steganography is having a covert communication between two parties whose existence is unknown to a possible attacker, a successful attack consists in detecting the existence of this communication (e.g., using statistical analysis of images with and without hidden information). Watermarking , as opposed to steganography, has the (additional) requirement of robustness against possible attacks. In this context, the term 'robustness' is still not very clear; it mainly depends on the application. Copyright marks do not always need to be hidden, as some systems use visible digital watermarks , but most of the literature has focused on imperceptible (e.g., invisible, inaudible) digital watermarks which have wider applications. Visible digital watermarks are strongly linked to the original paper watermarks which appeared at the end of the XIII century to differentiate paper makers of that time. Modern visible watermarks may be visual patterns
Steganography used in electronic communication include teganographic coding inside of a transport layer, such as an MP3 file, or a protocol, such as UDP.
Steganography is used by some modern printers, including HP and Xerox brand color laser printers. Tiny yellow dots are added to each page. The dots are barely visible and contain encoded printer serial numbers, as well as date and time stamps
Watermarking (now-a-days) is mainly used for copy-protection and copyright-protection Historically, watermarking has been used to send ``sensitive'' information hidden in another signal. Watermarking has its applications in image/video copyright protection.
Copy protection attempts to find ways, which limits the access to copyrighted material and/or inhibit the copy process itself. Examples of copy protection include encrypted digital TV broadcast, access controls to copyrighted software through the use of license servers and technical copy protection mechanisms on the media. A recent example is the copy protection mechanism on DVDs. However, copy protection is very difficult to achieve in open systems, as recent incidents (like the DVD hack - DeCss) show.
Copyright protection inserts copyright information into the digital object without the loss of quality. Whenever the copyright of a digital object is in question, this information is extracted to identify the rightful owner. It is also possible to encode the identity of the original buyer along with the identity of the copyright holder, which allows tracing of any unauthorized copies. The most prominent way of embedding information in multimedia data is the use of digital watermarking.
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