Digital Image Ballistics from JPEG Quantization
TR2008-638, Dartmouth College, Computer Science 2 Methods Using the Flickr API, 1,000,000 images were down- loaded from Flickr.com, a popular photo-sharing Digital Image Ballistics website. Since we are interested in the JPEG quan- from JPEG Quantization: tization table employed by different cameras, it A Followup Study was necessary to eliminate any images that had been edited or altered by any photo-editing soft- ware. To this end, only images tagged as “orig- inal” by Flickr were downloaded. Images were Hany Farid then eliminated if they were not 3-channel color Department of Computer Science images, and further eliminated if they had incom- Dartmouth College plete metadata, inconsistent “modification” and Hanover NH 03755 “original” dates, or a “software” metadata tag sug- gesting that the image had been edited by a photo- editing software. This filtering eliminated 557,045 Abstract images, leaving 442,955 images. The camera make, model, resolution, and JPEG The lossy JPEG compression scheme quantization table were extracted from each of the employs a quantization table that con- 442,955 images’ metadata. In order to further elim- trols the amount of compression achieved. inate possible edited or altered images, only those Because different cameras typically em- entries with five or more images having the same ploy different tables, a comparison of paired make, model, resolution, and quantization an image’s quantization scheme to a table were retained. This filtering eliminated 105,329 database of known cameras affords a images, leaving 337,626 images for the final anal- simple technique for confirming or deny- ysis.
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