Max Payne Correct Cd-rom

Classifications

There are many classifications of watermarks but the main ones are listed below

Of all these, we focus on the specific use classification. Thus, the watermarks can be used to avoid detection embedded message. To achieve this embedding of the message must distort slightly the carrier medium, this is done to avoid raising suspicion that there is something hidden. For example, if you hide information in a image and watermarked image is very distorted, then generate suspicion that the image has been modified causing the image is analyzed to see if there is information in it. So, to avoid detection of the embedded message must avoid distortions in the middle marking. In the watermarking techniques responsible for this is called concealment techniques information.

watermarks can be used to avoid removing the embedded message for this are used calls water marks robust. Such watermarks resist certain attacks made in the middle marking in this way are used to hide information from copyright protection and backup, among others. The

fragile watermarks and fragile semi are used to prevent forgeries marked the media. A feature of such schemes is, in contrast to the robust watermark, which can not withstand attacks and distortions made in the middle marking. If the media set is modified then the mark is lost, which is a possible forgery.

As we can see each of these types of watermarks are used for specific applications:

• concealment information is used by applications in which you want to keep secret information embedded. That is, these applications require a low impact perceptal (low distortion) to avoid suspicion.
• watermarks robust are used by applications that need resist distortion in the middle marking.
  
• The fragile watermark and semi-fragile are used by applications that verify the integrity or originality of the medium marked , do not stand for it distortions made to the media marked. ----------------
  

Before continuing ..... Let's attacks
attacks are classified as: Active Attacks

• : Distort or change the environment set to delete the message embedded or prevent the extraction function to find. Examples of these attacks are in pictures: compressions are loss (JPEG, GIF), filtered, changing contrast, brightness, histograms, geometric modifications (rotations, translations, mirror, etc) among others.

• Passive attacks: Analyze the means marking to determine the existence of a message, the size of it or just remove it. Examples of these attacks are visual and statistical attacks (Chi-square).
  

More will forward examples of such attacks. ----------------


The basic requirements a watermarking application are three:

1. Capacity: The maximum amount of information that can be hidden in a medium.
   
2. Robustness: The ability of a watermarking algorithm to extract the embedded message marking the medium after the latter has been attacked.
   
3. perceptual Impact: A watermarking algorithm is truly imperceptible if you can not tell at a glance the differences between the environment and marking the original media. While this capability is subjective in origin, there are metrics for evaluation. As an example, is the signal to noise ratio (PSNR), the mean square error (EMS), the correlation, the maximum absolute error (MAE), etc. Note that in order to assess this capability is necessary to compare the middle marked with the original media. As is usually distributed environment without marking the carrier medium is sufficient for the marked changes in the environment go unnoticed for the watermarking algorithm used is considered negligible.

Thus an application made to verify the integrity of medical images (for avoid changing ultrasound, X-ray images, etc..) requires low perceptual impact, a little strength and little ability, ie be located in the blue region (near the intersection of axes) of the following graph. This chart shows the relationship between these basic requirements.


On the other hand, an application to protect satellite images (copyright), needs to be resistant to different lossy compression schemes (ie the compressed image is not the same as the original image, since There was a loss in pixels eg JPEG). This resistance is needed because the potential thieves images, usually unaware of the existence of the brand (hidden message), then they proceed to try to eliminate it by changing the medium marked by avoiding leaving very distorted because they do not serve. This type of robust applications perceptually impact the environment marked as it is used a lot of redundancy of information (often repeat the same brand) and methods to store information much the distorting medium. Note that the ability of such schemes is minimal, as the redundancy decreases the capacity. The location of these schemes in the previous figure is close to the yellow and red.


Well ... dizzying enough of choro (bla bla bla) in the next post will make a watermarking scheme for images called LSB (Least Significant bit).

Be well, we are in contact ... Applications

Capacity Steganography perceptual impact LSB Robustness Requirements Watermarking Watermarking Watermarking Robust fragile