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Office documents and pictures contain lots of information in the meta tags that may deanonymize their author. Fotos may contain EXIF meta data like GPS location and a unique camera ID. Some webservices like the StolenCameraFinder are specialized for search images by meta information. The FBI tracked an Anonymous hacker using a foto with his girlfriend's boobs. Before uploading documents you should remove all meta data.
Meta tags in pictures and image files may be deleted in the file manager with a right-click. Choose the option "Remove meta tags" in the context menu. You may select and clean several files at once if you press the <CTRL>-key simultaneously. In the properties dialog of the file manager you may check the success of your attempt to delete the meta information.
You can use the Metadata Anonymisation Toolkit (MAT) to clean OpenOffice documents, Microsoft Office documents, PDFs and MP3 and FLAC sound files. Archives are supported too. Simply click with right mouse button on the file in the file manager and choose the entry "Metadata Anonymisation (MAT)".
Alternatively you may open the GUI of MAT. A menu entry you may find in the applications menu in the group "Utilities". Add the files you want to clean to list and click on the button "clean".
PDF documents are cleaned by rendering the layout internal and use this print layout for a new PDF without meta data. All images in the document are cleaned in this way but all formular data, content tables, links and so on are lost too.
Hint: MAT will clean only the master document of office documents. You have to clean embedded images by self before you use it.
MAT for documents and "exiv2" for fotos are useful tools to remove meta data from your own, self created files. Both can not anonymise the content, nor handle watermarking, steganography, or any overly customized metadata field/system from unknown source. You have to clean such documents more aggressively:
You may print the document with low resolution and scan it afterwards. For scanning of text documents you may use black/white color scheme and a low resolution too. Clean the scan images as descripted above.
You may convert PDFs and office documents to plain text files simply be right click the file in the file manager Thunnar. This text you can import in a new document and clean this new document as descripted above.
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