02-01-2013, 01:21 PM
Digital Image Forgery Detection Techniques for Still Images
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INTRODUCTION
The objective of this research is to develop a new forgery detection method that does not rely upon digital watermarks.
It is an area which has been researched by a number of scientists, but most notably - Alin C. Popescu and Hany Farid who developed a number of techniques.
Techniques include:
1) How light falls on objects within an image
2) Whether there are any areas of an image which has been “cloned” or “copied”
3) Looking for evidence of “retouching” in an image by detecting whether the pattern in the pixels have been destroyed
Three Core Areas of Research
Developing a new technique to detect changes and alterations to an image and does not rely on watermarks
Evaluate the algorithms used for image manipulation and to group them based upon their degree of manipulation. It is also important to consider image compression of image files in this area of work
An evaluation and comparison of the existing forgery detection techniques, and to carry out the evaluation along with defining a new grouping structure for forgery detection techniques
Digital Watermarks
Scientists, such as Alin C. Popescu and Hany Farid, have stated in their research papers about the vulnerability of watermarks in digital images in regards to authenticity of images
These drawbacks have made scientists to start looking for alternative methods in order to detect for “tell-tale” signs of tampering
Drawbacks of Digital Watermarks
It is not possible to determine whether the watermark has been inserted after manipulation
Watermarks can be fragile, and when a watermark image has been compressed with using a compressing algorithm like JPEG, they are destroyed
Extract a watermark manipulate the image and then reinsert the watermark, which itself can be modified during insertion therefore making the technique unreliable
Detecting areas where an image has been manipulated
Determining whether a manipulation is innocent, such as JPEG Compression and sharpening, from those which are malicious, such as adding or removing parts to an image. This is where watermarks have a difficulty – they are unable to determine this difference
What is a Forgery?
“Forgery” is a subjective word
An image can become a forgery based upon the context in which it is used
An image altered for fun or someone who has taken an bad photo, but has been altered to improve its appearance cannot be considered a forgery even though it has been altered from its original capture
The other side of forgery are those who perpetuate a forgery for gain and prestige – they create an image in which to dupe the recipient into believing the image is real and from this be able to gain payment and fame
Three type of forgery can be identified:
1) An image that is created using graphical software
2) An image where the content has been altered
3) An image where the context has been altered
Creating an image by altering its content is another method
Duping the recipient into believing that the objects in an image are something else from what they really are!
The image itself is not altered, and if examined will be proven as so
Altering Images
Altering images is not new – it has been around since the early days of photography
The concepts have moved into the digital world by virtue of digital cameras and the availability of digital image editing software
The ease of use of digital image editing software, which does not require any special skills, makes image manipulation easy to achieve and do
Digital Image Editors
Firstly, this research is not concentrating on any one make or brand of editor, but specifically the algorithms used
The algorithms are basically the tools which the photo editor uses to manipulate the image
Some of the tools found in the editors are: resizing an image, cropping, selecting part of an (lasso tool), removing unwanted parts of an image, rotating objects, merging pictures together