Beholder is a Discord moderation bot that scans images for text and inappropriate content.

Using OCR, Beholder extracts text from uploaded images, stickers, embeds and linked images, then compares the results against moderator-defined pattern lists. Messages matching configured rules can be deleted automatically, logged for review, or trigger moderation actions.

Beholder also supports NSFW image detection and image hash blocking, allowing moderators to quickly remove known unwanted content from their communities.

Beholder focuses on fast, privacy-conscious image moderation without storing user images.

Features

• OCR scanning of images, stickers, embeds and linked images
• Custom keyword and phrase matching
• Per-channel moderation rules
• NSFW image detection
• Image hash blocking and allow-listing
• Moderator review actions (block, unblock, timeout, kick, ban)
• Customisable moderation messages
• Discord log channel integration

Architecture

Beholder is split into separate processes for isolation.

The main bot connects to Discord and handles moderation decisions. NSFW detection is provided by nsfwd, a small local web service which keeps the TensorFlow model loaded in memory and accepts image scan requests from the bot.

OCR and image scanning are performed by tessd, which is spawned per request. This keeps untrusted image processing isolated from the main bot process. tessd runs under a separate user without access to the configuration file, and is constrained with memory and execution time limits, so malformed or hostile images cannot take down the bot or leak state between scans.

Compilation

mkdir build
cd build
cmake ..
make -j

Configuring the bot

Create a config.json in the directory above the build directory:

{
	"token": "token goes here",
	"log": "log path goes here",
	"environment": "environment name",
	"database": {
		"host": "localhost",
		"username": "mysql username",
		"password": "mysql password",
		"database": "mysql database",
		"port": 3306
	},
	"botlists": {
		"top.gg": {
			"token": "top.gg bot list token"
		},
		"other compatible bot list": {
			"token": "their token..."
		}
	}
}

Import the base MySQL schema:

mysql -u <database-user> -p <database-name> < database/schema.sql
Enter password:

Insert data into the database for your guild and moderation patterns.

Software Dependencies

• D++ v10.0.28 or later
• libcrypto/libssl
• libtesseract-dev
• libleptonica-dev
• ImageMagick Convert
• libmysqlclient 8.x
• g++ 11.4 or later
• libjsoncpp-dev
• tensorflow - Installation
• drogon
• libuuid
• zlib
• cmake
• fmtlib
• spdlog
• CxxUrl
• screen

Starting the bot

cd beholder
screen -dmS beholder ./run.sh

Starting the nsfw server

This daemon must be running to detect and delete NSFW imagery

cd beholder
screen -dmS nsfwd ./nsfwd.sh