Metadata - your files talk for you

Did you know this? When you send a document, a lot of data goes with it. But few Internet users are aware that many file formats contain hidden data, or metadata. Text processing files or PDFs are likely to contain the name of the author, the date and time of the creation of the file, and often even part of its editing history. The hidden data depend on the file format and the software used to create it.

Image file formats such as TIFF and JPEG are some of the most talkative ones. Created by digital cameras or mobile phones, these files contain metadata in a format called EXIF that may include the image’s date, time and even GPS coordinates, the model and serial number of the device that took it and a thumbnail of the original image. Image processing applications tend to keep this data intact. The Internet has countless cropped or pixelized images whose EXIF thumbnail still shows the original image. So, how do you rid your files of unwanted metadata and restore their virginity before sending them?

Checking and cleaning metadata

When you send a sensitive document, it is vital to ensure that its metadata are not compromising. There are various ways to access the metadata. The easiest way is to check the file properties. A simple right-click will give you a lot of information.

Desktop application files of the Office kind may contain information about the individual or company that that created the file. Whether you are using Microsoft Word or Open Office, you have the possibility of eliminating this information when you create the file.

PDF files can also act as snitches. They often contain the author’s name. It is accessible in the file properties and can be changed by using PDF file editing software. Using Acrobat Writer under Windows or Mac, you just have to go to the “File” menu and then “Properties” in order to modify the document author’s name. For GNU/Linux users, there are free alternatives such as PDF Mod that offer a simply way to edit PDF file metadata.

You can use the Exif Viewer extension for Firefox to display the metadata of JPEG images. It is also available for the Chrome browser. All this extension does is display Exif data.

Advanced control of metadata

There are more sophisticated tools that allow you to edit all kinds of metadata, regardless of the type of file – PDF, JPEG, GIF or anything else: -

  • MAT, Metadata Anonymisation Toolkit: an application with a graphical interface available under GNU/Linux
  • Metanull: an application with a graphical interface available under Windows
  • ExifTool: a command-line application available under GNU/Linux, Windows and Mac OS X.

This document was inspired by the Tails distribution’s official documentation, entitled “The Amnesic Incognito Live System.” Like the original, it is published under the GPL v 3.0 license.