unmasker finds content that survives inside a document but is hidden, covered, deleted, filtered, cropped or otherwise absent from what a person normally sees.

A black rectangle drawn over text is not a redaction. The page may look clean while the original text remains in the file and is still readable by a parser. unmasker reports that mismatch and stops there - evidence, not a verdict.

unmasker tests/specimens/pdf/libreoffice-writer-black-bars.pdf

  unmasker                                                      4 findings
    tests/specimens/pdf/libreoffice-writer-black-bars.pdf
  ────────────────────────────────────────────────────────────────────────

  ● 22 characters under a black shape at x 117.5-268.7, y           page 1
    684.2-698.5; the rest of the line still reads "Name:"
  │ human sees     ██████████████████████
  │ machine reads  Wanda Testowa-Przyklad

  ● 21 characters under a black shape at x 114.8-259.3, y           page 1
    664.5-678.7; the rest of the line still reads "Email:"
  │ human sees     █████████████████████
  │ machine reads  w.testowa@example.org

  ● 15 characters under a black shape at x 123.1-228.1, y           page 1
    644.7-658.9; the rest of the line still reads "Telephone:"
  │ human sees     ███████████████
  │ machine reads  +48 601 000 000

  ● 37 characters under a black shape at x 119.0-369.1, y           page 1
    624.9-639.2; the rest of the line still reads "Address:"
  │ human sees     █████████████████████████████████████
  │ machine reads  ul. Przykladowa 12/3, 00-001 Warszawa

  notes                                                             1 note
  ────────────────────────────────────────────────────────────────────────
    the file says it was made by Creator Writer; Producer LibreOffice
    24.2, and dates itself CreationDate 2026-08-31T20:25:50Z

  ────────────────────────────────────────────────────────────────────────
  searched 1 page of 1. 4 findings in 1 kind.
  sha256 fbaeef0d794f2bdb6f4c6bb823686a10d1e1b67e6b2d49df5fe33fd9a281f1a5

Every finding says what a human sees, what a machine reads, where the mismatch is and how the tool knows.

That file is a specimen committed to this repository, as is every other example on this page. Clone it and the commands run.

Installation

pipx install unmasker

Or:

uv tool install unmasker

Python 3.10 or later. The default install has one runtime dependency: pypdf. unmasker runs locally, makes no network requests and never modifies the file it is given.

From a checkout:

git clone https://github.com/osint-shifu/unmasker
cd unmasker
python3 -m venv .venv
.venv/bin/pip install -e .
.venv/bin/unmasker document.pdf

Usage

unmasker <file>   [options]
unmasker <folder> [options]

Scan one file:

unmasker document.pdf

Survey a folder:

unmasker ~/cases/kowalski

Produce machine-readable or shareable output:

unmasker document.pdf --json
unmasker document.pdf --md > report.md
unmasker ~/cases/kowalski --html > report.html

Exit status is part of the interface:

A file that could not be read is not a file that came back clean. unmasker keeps those states separate so a pipeline cannot silently treat failure as a clean result.

What it finds

Supported inputs are PDF, DOCX, ODT, XLSX, ODS, PPTX, ODP, JPEG and UTF-8 text. Content is identified from the file itself rather than trusted solely from the extension.

Practical examples

Text under an image

unmasker tests/specimens/pdf/libreoffice-writer-image-over-text.pdf

  unmasker                                                       1 finding
    tests/specimens/pdf/libreoffice-writer-image-over-text.pdf
  ────────────────────────────────────────────────────────────────────────

  ● 22 characters under an image at x 123.3-245.9, y 702.8-720.0;   page 1
    an image over a text layer is also what a scan of a printed
    page looks like, and there the two normally agree; the rest of
    the line still reads "Subject:"
  │ human sees     ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒
  │ machine reads  Ludmila Wieczorek-Test

  notes                                                             1 note
  ────────────────────────────────────────────────────────────────────────
    the file says it was made by Creator Writer; Producer LibreOffice
    24.2, and dates itself CreationDate 2026-08-31T23:50:46Z

  ────────────────────────────────────────────────────────────────────────
  searched 1 page of 1. 1 finding in 1 kind.
  sha256 d324105840b72c0d76c491150fe9220eabb4a87a3735afdb5de5af4c27fa0b66

An image over text is also what a scan of a printed page looks like. unmasker says so in the finding rather than calling it a redaction.

Hidden spreadsheet data

unmasker tests/specimens/xlsx/libreoffice-calc-hidden-columns.xlsx

  unmasker                                                      7 findings
    tests/specimens/xlsx/libreoffice-calc-hidden-columns.xlsx
  ────────────────────────────────────────────────────────────────────────

  comment                                                        1 finding
  ────────────────────────────────────────────────────────────────────────
  ● a comment by Halina Probna-Test, at a time the file does    whole file
    not state, carried in the file and not part of the
    document body
  │ human sees     nothing on the page
  │ machine reads  Panel agreed the reserve before the bids were opened.
  │                Not for the file we release.

  revision-history                                               1 finding
  ────────────────────────────────────────────────────────────────────────
  ● the file records 1 comment, by 1 person. A name here is     whole file
    whatever the application that wrote it was configured to
    say
  │ human sees     nothing on the page
  │ machine reads  Halina Probna-Test

  hidden-sheet                                                   1 finding
  ────────────────────────────────────────────────────────────────────────
  ● sheet "Workings" is marked hidden, and holds 1 value still  whole file
    in the file
  │ human sees     nothing on the page
  │ machine reads  Reserve set at 240,000. Kowalski came in 12% under; the
  │                others were told nothing.

  hidden-rows                                                    1 finding
  ────────────────────────────────────────────────────────────────────────
  ● row 4 of sheet "Evaluation" is hidden, and holds 6 values   whole file
    still in the file
  │ human sees     nothing on the page
  │ machine reads  Delta Consulting sp. z o.o. | 82 | 44 | 196000 | 63 |
  │                withdrawn after the deadline - do not list

  hidden-columns                                                 1 finding
  ────────────────────────────────────────────────────────────────────────
  ● column D of sheet "Evaluation" is hidden, and holds 5       whole file
    values still in the file
  │ human sees     nothing on the page
  │ machine reads  Reserve price (EUR) | 211000 | 238000 | 196000 | 251000

  undisclosed-metadata                                          2 findings
  ────────────────────────────────────────────────────────────────────────
  ● the creator field of docProps/core.xml holds a value the    whole file
    document does not show anywhere in its text
  │ human sees     nothing on the page
  │ machine reads  Halina Probna-Test

  ● the title field of docProps/core.xml holds a value the      whole file
    document does not show anywhere in its text
  │ human sees     nothing on the page
  │ machine reads  Tender evaluation - panel copy

  notes                                                             1 note
  ────────────────────────────────────────────────────────────────────────
    the file says it was made by Application
    LibreOffice/24.2.7.2$Linux_X86_64 LibreOffice_project/420$Build-2;
    AppVersion 15.0000, and counts revision 0; TotalTime 0

  ────────────────────────────────────────────────────────────────────────
  searched the text of this file. 7 findings in 6 kinds.
  sha256 6cb60d45c5e8fe7b2c05c1eee565ec417079909800f48209c88b28c42ec53c8e

Case-folder triage

unmasker tests/specimens/docx

  unmasker  tests/specimens/docx                              4 of 8 files
  ────────────────────────────────────────────────────────────────────────
    read      8 files, 17 findings
    not read  0 files

  what was found                                                  11 kinds
  ────────────────────────────────────────────────────────────────────────
    attached-file         1 file
    hidden-sheet          1 file
    zero-width            1 file
    bidi-control          1 file
    tag-characters        1 file
    mixed-script          1 file
    undisclosed-metadata  1 file
    metadata-path         1 file
    deleted-text          1 file
    comment               1 file
    revision-history      1 file

  files that hide something                                        4 files
  ────────────────────────────────────────────────────────────────────────
    libreoffice-writer-embedded-sheet.docx     attached-file, hidden-sheet
    libreoffice-writer-hidden-characters.docx  zero-width, bidi-control,
                                               tag-characters,
                                               mixed-script
    libreoffice-writer-metadata-leak.docx      undisclosed-metadata,
                                               metadata-path
    libreoffice-writer-tracked-changes.docx    deleted-text, comment,
                                               revision-history

  ────────────────────────────────────────────────────────────────────────
  searched 8 files. unmasker <file> for the detail, --json for all of it.

A directory scan reports what was read, what could not be read, which detector kinds appeared and which files contain findings. It does not rank files by "severity". Use the detailed file report or --json for every finding.

Read the rendered page back

unmasker scan.pdf --ocr

--ocr asks a different question: does the text stored in the document agree with the page after it is rendered? This can expose a hiding technique for which there is no dedicated detector yet.

For PDF page comparison it requires ghostscript and tesseract on PATH and costs seconds per page, so it is intentionally opt-in and refused for directory surveys.

Detector reference

The detector slug is stable output intended for reports and automation.

Page and rendering

Characters

Spreadsheets

Presentations

Images

Container, revisions and metadata

Evidence model

unmasker reports observable mismatches. It does not decide whether a document is malicious, manipulated or safe.

Each finding carries one of three evidence bases:

• direct - the relevant bytes are in the file and were read out directly
• circumstantial - the observation is consistent with hiding, but an innocent explanation can also fit
• self-reported - the document or application reports the fact about itself

There are no severity scores or synthetic confidence percentages. Different questions are not ranked against each other.

"Nothing found" and "nothing could be searched" are different results. unmasker keeps them separate. JSON exposes this explicitly through the searched field.

Values are not shortened with ellipses. If evidence is long, the report wraps it instead of silently dropping part of it.

Reports

The terminal report is for triage. Three stdout formats are available when the result needs to be stored, processed or sent to someone else:

• --json for automation
• --html for a self-contained human-readable report
• --md for Markdown-based systems

unmasker treats report content as untrusted because every quoted value came from a file being investigated. HTML values are escaped, Markdown evidence is fenced or escaped, and generated HTML contains no JavaScript or external resources.

The tool has no --out option. Redirection keeps the core rule simple: unmasker itself never writes to the input or to the case directory.

JSON and automation

--json writes one object on stdout while the exit status remains usable as a pipeline gate:

unmasker document.pdf --json > findings.json || echo "findings exist"

The JSON shape is versioned separately from the package version:

unmasker tests/specimens/pdf/libreoffice-writer-image-over-text.pdf --json

{
  "tool": "unmasker",
  "schema": "unmasker.scan/1",
  "version": "0.1.12",
  "file": "tests/specimens/pdf/libreoffice-writer-image-over-text.pdf",
  "sha256": "d324105840b72c0d76c491150fe9220eabb4a87a3735afdb5de5af4c27fa0b66",
  "kind": "pdf",
  "searched": true,
  "remarks": [
    "the file says it was made by Creator Writer; Producer LibreOffice 24.2, and dates itself CreationDate 2026-08-31T23:50:46Z"
  ],
  "findings": [
    {
      "detector": "text-under-image",
      "basis": "direct",
      "summary": "22 characters under an image at x 123.3-245.9, y 702.8-720.0; an image over a text layer is also what a scan of a printed page looks like, and there the two normally agree; the rest of the line still reads \"Subject:\"",
      "human_sees": "▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒",
      "machine_reads": "Ludmila Wieczorek-Test",
      "location": {
        "page": 1
      },
      "codepoints": [
        "U+004C",
        "U+0075",
        "U+0064",
        "U+006D",
        "U+0069",
        "U+006C",
        "U+0061",
        "U+0020",
        "U+0057",
        "U+0069",
        "U+0065",
        "U+0063",
        "U+007A",
        "U+006F",
        "U+0072",
        "U+0065",
        "U+006B",
        "U+002D",
        "U+0054",
        "U+0065",
        "U+0073",
        "U+0074"
      ]
    }
  ]
}

The /1 changes only when the JSON shape changes incompatibly. A normal package release does not force downstream consumers to guess whether their parser still works.

Design principles

• Evidence, not verdicts. Report what can be shown and leave interpretation to the analyst.
• Absence is explicit. Unreadable, unsearched and searched-with-no-findings are different states.
• Read-only. Input files are never modified.
• Local. No uploads and no network requests.
• Real specimens. Detectors are tested against files produced by real applications, not only hand-built fixtures.
• No hidden ranking. Findings are grouped by what was observed, not by an invented severity score.

What unmasker is not

unmasker is not a malware scanner, DLP system, authenticity classifier or forensic verdict engine. It exposes discrepancies and residual content so a human or a downstream system can decide what they mean.

How it is tested

Every detector fires on a committed specimen written by a real producer, including LibreOffice, headless Chrome, Ghostscript, Tesseract, exiftool and ImageMagick. There are 38 of them and each has a provenance note describing how it was produced, what a person sees and what is actually stored inside.

This matters because real producers routinely disagree with assumptions made from a file-format specification. The first PDF specimen, for example, showed that LibreOffice represented a redaction bar differently from the shape the initial detector design expected.

Independent tooling such as Poppler is used where specimens need measurements, and detector behavior is mutation-tested so a broken rule has to break a test. The README is checked against the repository so the front page cannot silently drift away from the code: the detector list, the detector badge, the specimen count, the test count, and every example on this page - each command is run and its output compared to the block printed beneath it.

748 tests.

Limits

• No verdicts about whether a document was manipulated or malicious.
• No writing to the input file and no network access.
• Legacy OLE2 formats such as .doc, .xls and .ppt are not supported.
• Signature coverage is not checked. A signed PDF's /ByteRange says which bytes it covers, and no signed specimen could be produced to test a detector against.
• XMP is read in PDF and JPEG. DOCX and TIFF carry packets too and are not read yet.
• Producer coverage is not universal. Microsoft Word and Adobe Acrobat are not part of the current specimen corpus, and different producers can encode the same feature differently.
• OCR is optional, slower than structural detection and depends on external tools.

See tests/specimens/README.md for the current producer coverage and explicitly documented gaps.

Development

git clone https://github.com/osint-shifu/unmasker
cd unmasker
python3 -m venv .venv
.venv/bin/pip install -e ".[dev]"
.venv/bin/pytest
.venv/bin/ruff check .
.venv/bin/mypy

Project references:

• CONTRIBUTING.md - development and specimen rules
• SECURITY.md - security policy and threat model
• CHANGELOG.md - release history
• tests/specimens/README.md - specimen provenance and coverage gaps

License

Apache License 2.0.