On message stub Ph.D thesis and on the title page M.Sc degree

Thesis (M.Sc.) - Cairo University - National Institute of Laser Enhanced Science (NILES) - Department of Laser Applications in Environmental Metrology Photochemistry and Agriculture

Questioned documents examination (QDE) is considered a practical branch of forensic sciences. It is concerned with signatures, handwriting, typewriting, as well as laser printers and photocopiers outputs.The simplicity of using laser printers and photocopiers and its high resolution made them used on a large scale in the counterfeiting and forgery by alteration and/or addition in questioned documents. In the present work, Video Spectral Comparator (VSC), as a common technique in forensics laboratories and laser-induced breakdown spectroscopy (LIBS), as a spectrochemical analytical technique were used to differentiate between different black toners of printers and photocopiers given their absorption and reflection of light, and their elemental composition.The principal component analysis (PCA) chemometric method was used to analyze the spectroscopic data statistically. Measurements were performed on twenty-three different printers and photocopiers (brands and models). VSC investigation is based on different photochemical absorption and reflection properties of toners samples. The LIBS spectra were compared to characterize each toner type. The multivariate statistical analysis based on Principal Component Analysis (PCA) has developed a model of discriminating the toners in questioned documents. Results revealed that VSC offers relatively poor discrimination capability at the same time LIBS has succeeded in the discrimination between different toner types of printers and photocopiers brands. However, it has little power to discriminate between toners of different models of the same brand

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