Gemini Watermark Tool is a lightweight, standalone command-line utility that removes Gemini Nano Banana / Pro watermarks from images using mathematically accurate reverse alpha blending.

• Fast & offline: single executable, zero dependencies
• Flexible workflows: in-place editing, explicit input/output, and batch directory processing
• Cross-platform: Windows / Linux / macOS / Android
• Auto detection: detects 48×48 vs 96×96 watermark size automatically

• Batch Processing - Process entire directories at once
• One-Click Removal - Simply drag & drop an image onto the executable
• In-Place Editing - Process files directly without specifying output
• Deterministic (Not Inpainting) - Restores pixels via reverse alpha blending (no guessing)
• Cross-Platform - Windows, Linux, macOS, and Android
• Zero Dependencies - Single standalone executable, no installation required
• Auto Size Detection - Automatically detects 48×48 or 96×96 watermark size
• Mathematically Accurate - Precise restoration using reverse alpha blending

Best for: slides, documents, UI screenshots, diagrams, logos.

Focus on the bottom example (text-heavy slide).
Generative inpainting often breaks text: warped edges, wrong spacing, invented strokes.
GeminiWatermarkTool reverses the blending equation to recover pixels, keeping text crisp.

Important: This tool removes visible watermarks only. It does NOT remove SynthID.

SynthID is Google DeepMind's invisible watermarking technology embedded in AI-generated images. Unlike visible watermarks:

• Invisible to human eyes
• Integrated during generation (not added afterward)
• Extremely robust against common image manipulations

Our extensive research revealed a fundamental truth:

SynthID is not a watermark added to an image — it IS the image.

SynthID operates as a Statistical Bias during generation. Every pixel choice is subtly influenced by Google's private key using Tournament Sampling. The watermark and visual content are inseparably bound.

Visible Watermark:  Image + Overlay = Result     ✓ Removable (this tool)
SynthID:            Biased Generation = Image    ✗ Cannot separate

Conclusion: Removing SynthID while preserving image quality is currently not feasible.

📄 Full SynthID Research Report →

• SynthID Image Watermark Research Report

Download the latest release from the Releases page.

USE AT YOUR OWN RISK

This tool modifies image files. While it is designed to work reliably, unexpected results may occur due to:

• Variations in Gemini's watermark implementation
• Corrupted or unusual image formats
• Edge cases not covered by testing

Always back up your original images before processing.

The author assumes no responsibility for any data loss, image corruption, or unintended modifications. By using this tool, you acknowledge that you understand these risks.

1. Download GeminiWatermarkTool-Windows-x64.exe
2. Drag an image file onto the executable
3. Done! The watermark is removed in-place

# Simple mode - edit file in-place
GeminiWatermarkTool watermarked.jpg

# Specify output file
GeminiWatermarkTool -i watermarked.jpg -o clean.jpg

# Batch processing
GeminiWatermarkTool -i ./input_folder/ -o ./output_folder/

The easiest way to use this tool - just provide a single image path:

GeminiWatermarkTool image.jpg

This will remove the watermark in-place, overwriting the original file.

⚠️ Warning: Simple mode overwrites the original file permanently. Always back up important images before processing.

For more control, use the -i (input) and -o (output) options:

# Single file
GeminiWatermarkTool -i input.jpg -o output.jpg

# With explicit --remove flag (optional)
GeminiWatermarkTool -i input.jpg -o output.jpg --remove

Process all images in a directory:

GeminiWatermarkTool -i ./watermarked_images/ -o ./clean_images/

• Input: directory
• Output: directory
• Supported formats: .jpg, .jpeg, .png, .webp, .bmp

The tool automatically detects the appropriate watermark size based on image dimensions:

Use --force-small or --force-large to override automatic detection.

# Just remove the watermark, keep the same filename
GeminiWatermarkTool photo_from_gemini.jpg

# Save to a new file, keeping the original intact
GeminiWatermarkTool -i original.jpg -o cleaned.jpg

# Process all images in a folder
GeminiWatermarkTool -i ./gemini_outputs/ -o ./processed/

# See detailed processing information
GeminiWatermarkTool -i image.jpg -o output.jpg -v

All binaries are statically linked with no external runtime dependencies.

The watermark is semi-transparent. If the original background was similar to the watermark color, the difference may be subtle. Try viewing at 100% zoom in the watermark area (bottom-right corner).

Use --force-small or --force-large to manually specify:

GeminiWatermarkTool -i image.jpg -o output.jpg --force-small

Make sure the output path is writable and the file isn't open in another program.

• Only removes Gemini visible watermarks (the semi-transparent logo in bottom-right)
• Does NOT remove SynthID invisible watermarks — see why
• Designed for Gemini's current watermark pattern (as of 2025)

# Clone vcpkg
git clone https://github.com/microsoft/vcpkg.git
cd vcpkg

# Bootstrap
./bootstrap-vcpkg.sh    # Linux/macOS
.\bootstrap-vcpkg.bat   # Windows

# Set environment variable
export VCPKG_ROOT="$HOME/vcpkg"       # Linux/macOS (add to .bashrc)
$env:VCPKG_ROOT = "C:\vcpkg"          # Windows PowerShell

The project uses CMakePresets.json for cross-platform configuration.

# List available presets
cmake --list-presets

cmake --preset windows-x64-Release
cmake --build --preset windows-x64-Release

cmake --preset linux-x64-Release
cmake --build --preset linux-x64-Release

macOS requires separate builds for each architecture:

# Build x64
cmake -B build-x64 -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_TOOLCHAIN_FILE=$VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake \
  -DVCPKG_TARGET_TRIPLET=x64-osx \
  -DCMAKE_OSX_ARCHITECTURES=x86_64
cmake --build build-x64

# Build arm64
cmake -B build-arm64 -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_TOOLCHAIN_FILE=$VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake \
  -DVCPKG_TARGET_TRIPLET=arm64-osx \
  -DCMAKE_OSX_ARCHITECTURES=arm64
cmake --build build-arm64

# Create Universal Binary
lipo -create build-x64/GeminiWatermarkTool build-arm64/GeminiWatermarkTool \
  -output GeminiWatermarkTool

Requires Android NDK:

export ANDROID_NDK_HOME="/path/to/android-ndk"

cmake --preset android-arm64-Release
cmake --build --preset android-arm64-Release

cmake -B build -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_TOOLCHAIN_FILE=$VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake \
  -DVCPKG_TARGET_TRIPLET=x64-linux

cmake --build build

gemini-watermark-tool/
├── CMakeLists.txt              # Main build configuration
├── CMakePresets.json           # Cross-platform build presets
├── vcpkg.json                  # Dependencies manifest
├── src/
│   ├── main.cpp                # CLI entry point
│   ├── watermark_engine.cpp    # Core watermark processing
│   ├── watermark_engine.hpp
│   ├── blend_modes.cpp         # Alpha blending algorithms
│   ├── blend_modes.hpp
│   └── ascii_logo.hpp          # ASCII art banner
├── report/
│   └── synthid_research.md     # SynthID research documentation
└── resources/
    ├── app.ico                 # Windows application icon
    └── app.rc.in               # Windows resource template

All dependencies are managed via vcpkg and statically linked:

Gemini applies visible watermarks using alpha blending:

watermarked = α × logo + (1 - α) × original

By statistically analyzing and comparing values related to Alpha, we can reconstruct an Alpha Map that is either correct or very close to it.

Solving for the original pixel:

original = (watermarked - α × logo) / (1 - α)
         = (watermarked - alpha_map) / (1 - α)

This mathematical inversion produces exact restoration of the original pixels.

This tool is provided for personal and educational use only.

The removal of watermarks may have legal implications depending on your jurisdiction and the intended use of the images. Users are solely responsible for ensuring their use of this tool complies with applicable laws, terms of service, and intellectual property rights.

The author does not condone or encourage the misuse of this tool for copyright infringement, misrepresentation, or any other unlawful purposes.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY CLAIM, DAMAGES, OR OTHER LIABILITY ARISING FROM THE USE OF THIS SOFTWARE.

MIT License

Allen Kuo (@allenk)

• Removing Gemini AI Watermarks: A Deep Dive into Reverse Alpha Blending
• SynthID Image Watermark Research Report
• SynthID Research Report — Why invisible watermarks cannot be removed

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