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Acronyms & Terms Used In Forensic Document Examination

Anne Smith • July 12, 2022

Types of File Formats:

Note: hyperlinks listed were accessed August 2020


 PDF

Portable Document Format files are not image files. They "capture formatting information… making it possible to send formatted documents and have them appear on the recipient’s monitor or printer as they were intended." PDFs can be created using scanners, printer properties, PDF software, and internal computer software like MS word. Pages are usually created at either 150 ppi or 300 ppi and compressed using algorithms. The process creates a series of artifacts is commonly referred to a pixelation.

https://www.jetpressfl.com/file-preparation/print-file-formats/ , et al.

 

TIF/TIFF

Tagged Image File Format: "uses lossless compression to maintain image integrity and clarity." In lossless compression, little/no image data is lost during the compression process.

https://www.jetpressfl.com/file-preparation/print-file-formats/ , et al.

 

JPEG/JPG

Joint Photographic Experts Group: "image file format… uses lossy compression

(lossy meaning “with losses to quality”).  JPG data, when compressed, leads to a decrease in image quality if image is enhanced in any way.

https://www.jetpressfl.com/file-preparation/print-file-formats/, et al.

 

DPI, PPI, Pixel and Pixelation

 

DPI

Dots Per Inch: "is a measure of…image scanner dot density, in particular the number of individual dots that can be placed in a line within the span of 1 inch."

https://en.wikipedia.org/wiki/Dots_per_inch

 

PPI

Pixels Per Inch: "are measurements of the pixel density (resolution) of an electronic image device, such as a computer monitor…, or image digitizing device such as a camera or image scanner. Horizontal and vertical density are usually the same, as most devices have square pixels…" PPIs are closely related to DPIs.

https://en.wikipedia.org/wiki/Pixel_density

 

Pixel

"Short for Picture Element" 1, "a pixel is generally thought of as the smallest single component of a digital image…To represent color images, separate red, green and blue components are used for each pixel, and so the pixel 'value' is a vector of three triad numbers."2 A pixel is "equivalent to roughly 1⁄96 inch (0.26 mm)"3.

In Photoshop CC digitized documents are opened in RGB image mode.

 

Consider pixels like Pointillism, "a neoimpressionist painting technique, from the late 19th century, using tiny dots of various pure colors, which became blended in the viewer's eye. The technique relied on systematic calculation and scientific theory to achiever predetermined visual effects"4, too.

1https://www.webopedia.com/TERM/P/pixel.html

2 https://htm.fandom.com/wiki/Pixel

3https://en.wikipedia.org/wiki/Pixel

4https://www.britannica.com/art/Neo-Impressionism

 

Pixelation

A noun used to describe "the display of a digitized image such that the pattern of pixels is obvious to the naked eye".1  Pixelation is the common term used, which refers to process creates a series of artifacts. Evidence of pixelation/artifacts can be observed using variety of scientific-based techniques. "An image artifact is any feature which appears in an image which is not present in the original imaged object.  An image artifact is sometime the result of improper operation of the imager."2

1http://www.kirkmahoney.com/blog/2009/05/pixilation-vs-pixelation/

2https://www.cis.rit.edu/htbooks/mri/chap-11/chap-11.htm

 

Algorithm, Metadata and Metadata Analysis

 

Algorithm

"Algorithms resemble recipes. Recipes tell you how to accomplish a task by performing a number of steps… An algorithm is an unambiguous description that makes clear what has to be implemented."

https://fiftyexamples.readthedocs.io/en/latest/algorithms.html#:~:text=However%2C%20%E2%80%9Calgorithm%E2%80%9D%20is%20a%20technical%20term%20with%20a,produce%20the%20correct%20result.%20...%20More%20items..

 

Metadata

"Metadata is data about data…it's information that's used to describe the data that's contained in something like a…document...Metadata is data that describes data, but it isn't the data itself.

 

Think of metadata as a card file in your childhood library that contains information about a book; metadata isn't the book itself. You can learn a lot about a book by examining its card file, but you have to open the book to read it."

https://www.lifewire.com/metadata-definition-and-examples-1019177

 

Metadata Analysis

Using computer software to examine metadata in order to determine essential features found within a document file by separating it into component parts. Determining if a document contains copied and pasted sections/parts is a function of metadata analysis.

 

Cut-and-Paste (C&P) and Copy-and-Paste (CP)

 

C&P

Computer commands for 'cut' and 'paste', move text or data or a digital image from one place in an electronic document or computer system to another electronic document or computer system. "…the cut and copy operation is destructive in nature and if not executed properly, could lead to data loss."  Can be used as a noun, a verb, or an adjective.

https://www.techopedia.com/definition/6299/cut-and-paste-cp

 

CP

Computer commands for 'copy' and 'paste', copy text or data or a digital image from one place in an electronic document or computer system to another electronic document or computer system. "Unlike cut and paste,…copy and paste creates a duplicate in the new location." Can be used as a noun, a verb, or an adjective.

https://www.techopedia.com/definition/6299/cut-and-paste-cp

 

Digital Image, Digital Image Vector File and Raster Files

 

Digital Image

"Is formed from the pixels and the device used to capture the digital image." A digital camera and a scanner are devices that capture digital images, which are identified by the file format names "… JPEG… TIFF…".

https://www.educba.com/what-is-digital-image/

 

Digital Image Vector Files


are text data which can be enlarged or reduced without pixelation. “Vector images are…created in in Adobe Illustrator” and other programs as well. Vector images are typically saved as…PDF" document file, allowing each image to be as crisp and clear as the original.

https://mariahalthoff.com/blog/raster-vs-vector-files


Digital Image Raster Files


…are images created by pixels. Each pixel is assigned a color…Raster files are typically saved as…JPEG…"1 image files. "Advanced raster editors, like GIMP (free) and Adobe Photoshop…are equipped to deal with raster images down to the pixel."2 These editors create layers, which can be flattened. This means the program "condenses all the image layers into one single layer"3. After the layer is saved it cannot be reopened with layers.

1https://mariahalthoff.com/blog/raster-vs-vector-files, et al.

2https://en.wikipedia.org/wiki/Raster_graphics_editor

3https://www.techwalla.com/articles/what-does-it-mean-to-flatten-your-photoshop-image

 

Image Anomalies

 

"Deviations from the common…arrangement or form" are irregularities and inconsistencies between and among digital images, which may be far removed (generationally speaking) from the original. For example, pixel colors range from barely visible in a PDF made from an original document to varying shades of light to dark gray around areas of interest (AOI) in a (multi-generation) questioned PDF document.

https://www.dictionary.com/browse/anomalies

 

Computer Software Applications (apps)

 

Adobe Acrobat Pro DC

"… used to create, edit, manipulate, sign, print, organize, and track PDF files" and export digital images within a PDF file.

https://www.lifewire.com/adobe-acrobat-software-1077212

 

Adobe Photoshop CC

Forensic document examination industry standard with "one of the most advanced and popular image editors in the world." Screens can be enlarged 12,800%.

https://adobe-photoshop.en.softonic.com/

 

Affinity Publisher

“…this incredibly smooth, intuitive app gives you the power to combine your images, graphics and text to make…[new] layouts ready for publication.

https://affinity.serif.com/en-us/publisher/

 

Microsoft Word (MS Word) & PowerPoint Presentation (PPT)

"The most widely used tools for working with documents and presentations". MS Word screens can be enlarged up to 500%; PPT screens up to 400%.

https://microsoft-word.en.softonic.com/

 

SnagIt

"A comprehensive screen capturing tool…Once captured, your image is stored and ready for editing or sending…file formats as…PDF…and JPG" and TIFF, among others.  https://snagit.en.softonic.com/


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