OPENING METADATA MANUAL...
SCANNING FILES, PHOTOS, DOCUMENTS, HEADERS...
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METADATA :: HIDDEN DATA IN FILES

> Metadata is data about data.
> It can reveal when, where, how, and by whom a file, message, or photo was created.

TL;DR: Before sharing files online, remember that photos, PDFs, Office documents, emails, and archives can contain hidden information. Metadata is not always dangerous, but it can leak names, usernames, software, device models, GPS coordinates, edit history, timestamps, and internal paths.

WHAT IS METADATA?

Metadata is information attached to a file or communication. It does not always appear in the visible content, but it can still be read by software, websites, investigators, platforms, or anyone who receives the file.

A document may look clean, but still contain the author name. A photo may show only a landscape, but still include the GPS location. An email may look simple, but its headers can reveal routing information and mail servers.

PHOTOS

Camera model, timestamp, GPS location, orientation, editing software, sometimes device serial-related information.

DOCUMENTS

Author, company, template path, revision count, comments, tracked changes, software version, creation and modification dates.

EMAILS

Headers, sender path, mail servers, timestamps, authentication results, message IDs, and sometimes client information.

WHY IT MATTERS

Metadata can connect a file to a person, a device, an organization, a place, or a timeline. For everyday sharing, it may not matter. For privacy-sensitive work, journalism, activism, internal company documents, or public posting, it can matter a lot.

Metadata is not always bad. It can be useful for sorting photos, proving document history, or troubleshooting systems. The problem starts when metadata is shared unintentionally.

COMMON METADATA LEAKS

EXIF IN PHOTOS

Smartphones and cameras can store GPS coordinates, shooting date, camera model, lens data, orientation, and editing software in image files.

PDF PROPERTIES

PDFs may include author names, creator tools, timestamps, embedded comments, previous versions, hidden layers, or form data.

OFFICE DOCUMENTS

Word, Excel, and PowerPoint files can contain authors, reviewers, hidden comments, tracked changes, custom properties, and embedded objects.

CHECK FILE METADATA

On Linux, macOS, or Windows, one of the most useful tools is exiftool. It can inspect a wide range of file types.

cluster@metadata:~$ inspect-file

# Show metadata
exiftool photo.jpg
exiftool document.pdf
exiftool report.docx

# Show only GPS-related metadata
exiftool -gps:all photo.jpg

# Show author-related fields
exiftool -Author -Creator -Producer -Company document.pdf

REMOVE METADATA FROM PHOTOS

For images, remove metadata before publishing or sending them to people who do not need the extra information.

# Remove all metadata from a copy
exiftool -all= -o clean.jpg original.jpg

# Remove GPS data only
exiftool -gps:all= photo.jpg

# Remove metadata from every JPG in a folder
exiftool -all= *.jpg

Some platforms remove part of the metadata when uploading images, but do not rely on that for sensitive files. Clean the file yourself before upload.

REMOVE METADATA FROM PDF FILES

PDFs are tricky because metadata can be stored in several ways: document properties, embedded objects, comments, form fields, hidden layers, or previous edits.

# Basic PDF metadata removal with exiftool
exiftool -all= -o clean.pdf original.pdf

# Safer method: export/print to a new PDF
# Open the document, print to PDF, then check the new file again.

For sensitive PDFs, do not only remove metadata fields. Also check comments, hidden text, tracked changes, attachments, form data, and redactions.

OFFICE DOCUMENTS

Office files can contain hidden content even when the visible document looks clean. Use the built-in document inspector before sharing.

cluster@metadata:~$ office-cleanup

Microsoft Office:
File > Info > Check for Issues > Inspect Document

LibreOffice:
File > Properties
File > Export As > Export as PDF

Before sharing:
- remove comments
- accept or reject tracked changes
- remove hidden sheets or hidden slides
- check document properties
- export a clean copy

EMAIL METADATA

Email contains headers. Headers are useful for routing, spam filtering, authentication, and troubleshooting, but they also contain technical traces such as timestamps, mail servers, message IDs, and sometimes client details.

End-to-end encryption can protect message content, but it usually does not hide all metadata. Sender, recipient, subject, timing, and server-level traces may still exist depending on the system.

SCREENSHOTS VS PHOTOS

A screenshot often contains less camera metadata than a photo, but it can still leak information visually: usernames, tabs, browser bookmarks, notifications, internal URLs, ticket numbers, IP addresses, paths, or customer data.

PHOTO RISK

GPS coordinates, device model, timestamp, visible background, reflections, badges, screens, documents, or location clues.

SCREENSHOT RISK

Open tabs, account names, internal tools, notifications, browser extensions, URLs, tokens, private messages, or admin panels.

PRACTICAL CHECKLIST

Inspect files before publishing them.
Remove EXIF data from photos before public upload.
Use document inspector tools before sharing Office files.
Export a clean PDF instead of sharing editable documents when possible.
Never rely only on black rectangles for redaction. Use proper redaction tools.
Check screenshots for visible private information.
Keep an original copy privately, then share a cleaned copy.
For sensitive work, use a dedicated workflow or a separate device/profile.

USEFUL TOOLS

EXIFTOOL

Powerful command-line tool to read and remove metadata from many file types.

MAT2

Metadata Anonymisation Toolkit. Useful for cleaning common file formats on Linux.

DOCUMENT INSPECTOR

Built-in Microsoft Office feature to find comments, author names, hidden content, and document properties.

MINIMAL SAFE WORKFLOW

1. Keep the original file private.
2. Create a copy for sharing.
3. Inspect metadata with exiftool or a document inspector.
4. Remove unnecessary metadata.
5. Re-open and verify the cleaned file.
6. Share the clean copy, not the original.

SOURCES

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