JPEGsnoop - JPEG File Decoding Utility

Introduction

Every digital photo contains a wealth of hidden information -- JPEGsnoop was written to expose these details to those who are curious.

Not only can one determine the various settings that were used in the digital camera in taking the photo (EXIF metadata, IPTC), but one can also extract information that indicates the quality and nature of the JPEG image compression used by the camera in saving the file. Each digical cameras specifies a compression quality levels, many of them wildly different, leading to the fact that some cameras produce far better JPEG images than others.

What can I do?

Check out a few of the many possible uses for JPEGsnoop!

One of the latest features in JPEGsnoop is an internal database that compares an image against a large number of compression signatures. JPEGsnoop reports what digital camera or software was likely used to generate the image. This is extremely useful in determining whether or not a photo has been edited / tampered in any way. If the compression signature matches Photoshop, then you can be pretty sure that the photo is no longer an original! This type of analysis is sometimes referred to as Digital Image Ballistics / Forensics. 

JPEGsnoop reports a huge amount of information, including: quantization table matrix (chrominance and luminance), chroma subsampling, estimates JPEG Quality setting, JPEG resolution settings, Huffman tables, EXIF metadata, Makernotes, RGB histograms, etc. Most of the JPEG JFIF markers are reported. In addition, you can enable a full huffman VLC decode, which will help those who are learning about JPEG compression and those who are writing a JPEG decoder.

Other potential uses: determine quality setting used in Photoshop Save As or Save for Web settings, increasing your scanner quality, locating recoverable images / videos, decoding AVI files, examining .THM files, JPEG EXIF thumbnails, extract embedded images in Adobe PDF documents, etc.

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File Types Supported

JPEGsnoop will open and attempt to decode any file that contains an embedded JPEG image, such as:

• .JPG - JPEG Still Photo
• .THM - Thumbnail for RAW Photo / Movie Files
• .AVI* - AVI Movies
• .DNG - Digital Negative RAW Photo
• .CRW, .CR2, .NEF, .ORF, .PEF - RAW Photo
• .MOV* - QuickTime Movies, QTVR (Virtual Reality / 360 Panoramic)
• .PDF - Adobe PDF Documents

轉自 http://www.impulseadventure.com/photo/jpeg-snoop.html