U.S. flag

An official website of the United States government, Department of Justice.

Source Camera Identification for Heavily JPEG Compressed Low Resolution Still Images

NCJ Number
Journal of Forensic Sciences Volume: 54 Issue: 3 Dated: May 2009 Pages: 628-638
Erwin J. Alles M.Sc.; J.M.H. Geradts Ph.D.; Cor J. Veenman Ph.D.
Date Published
May 2009
11 pages
This study examined whether the source camera for heavily JPEG compressed digital photographs of resolution 640 x 480 pixels could be identified by analyzing Photo Response Non-Uniformity (PRNU), which involves the identification of small differences in production conditions for each separate camera sensor, resulting in small variations in pixel size and performance that constitute a fixed pattern within the sensor.
The study found that the PRNU is unique even among cameras of the same type. The identification of source cameras based on PRNU is possible despite heavy JPEG compression that suppresses high-frequency signals such as PRNU. In order to remove DCT (discrete cosine transform)-block edge artifacts introduced by JPEG compression, the authors propose the simple method of averaging multiple pixels into one macro element. This method proved more effective than previously reported methods. The techniques proposed can readily be applied to video footage as well. The research showed that simple and computationally efficient techniques enabled source-camera identification, especially for the closed-set problem. This involves PRNU extraction with a two-dimensional Gaussian filter, detection by calculating a correlation coefficient, JPEG edge artifact suppression by pixel averaging, and scene content suppression by thresholding. The open-set problem performance, however, must be improved. Future work will involve both improving the performance of the identification scheme used in the current research and extending it to different situations and applications. 4 tables, 9 figures, and 12 references