David Mann <[email protected]> wrote: > On Oct 1, 2015, at 10:04 am, Mark Roberts <[email protected]> wrote: > >> If someone does steal an image outright, removal of the watermark >> works against them in court and can net you extra damages. > > If you can even get them to court, nevermind afford the lawyers to try.
There are ways to watermark that are quite hard to detect or remove. Quoting text I wrote most of at : http://en.citizendium.org/wiki/Steganography#Digital_watermarking Encryption is often used as one of the steps in steganographic hiding of information. Consider an image file with 10 megapixels, each 8 bits, in which you want to hide a message of a few megabits. The simplest way to do it is to just put the message in the least significant bits of each pixel. However, that has several disadvantages: it can be detected by an enemy who checks those bits (since they will be non-random), an enemy who finds it can read it (since it is not encrypted), and the message can be removed from the image by overwriting those bits. If you encrypt the message before inserting it in the image then — since the output of any good cipher is apparently random — it generally becomes very difficult for any enemy who does not have the encryption key to detect the message, or to read it if he does detect it. Note, however, that if the low-order bits are initially non-random then replacing them with random material is easily detected; this might occur for example with a low-cost camera that puts real data only in the high six bits of an 8-bit pixel. Generally symmetric key cryptography is used in such applications. For example, when a media company embeds a watermark in a video as part of a DRM system, it is often encrypted so only that company, or agents to whom it has provided the key, can recover it. ... Often some sort of transform is applied to the cover file before the steganographic data is added. Many different transforms can be used; among the commonest are the Fourier transform for sound data and discrete cosine transform for images or video. The sequence is then: apply the transform to the input data embed the encrypted message apply the inverse transform to produce the output data Choice of transform is a rather complex question. ... /end quote That sort of trickery can give a watermark that is quite difficult to detect or remove, but easily proven in a court case. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
