Tesseract OCR Image Text Extraction

Extract text from images using Tesseract.js (OCR). Supports multi-language recognition including Chinese and English, region recognition, character whitelist filtering, text orientation detection, and can run in a Node.js environment.

Extract text content from images based on Tesseract.js (the WebAssembly port of the Tesseract OCR engine).

Use Cases

Use when users need "image to text," "OCR recognition," "extract text from images," "screenshot character recognition," "scan to text," or "image text orientation detection."

Core Capabilities

• Recognize text from local images or image URLs
• Support for 100+ languages, with the ability to specify multiple languages simultaneously (e.g., ['eng', 'chi_sim'])
• Support for specifying recognition regions (--rectangle), character whitelists (--whitelist)
• Support for text orientation and script detection (--detect)
• Support for switching page segmentation modes (--psm) and OCR engine modes (--oem)
• Output formats: text (default), hocr, blocks (JSON), tsv

Limitations

• Does not support PDF files
• Does not modify the Tesseract recognition model to improve accuracy
• Requires a Node.js environment (this Skill uses Node.js scripts)

---

Workflow

1. Confirm Environment

node -v && npm ls tesseract.js 2>/dev/null || echo "tesseract.js not installed"

If not installed:

cd /root/.openclaw/workspace/skills/tesseract-ocr && npm init -y > /dev/null 2>&1 && npm install tesseract.js

2. Execute Recognition

Basic command:

node scripts/ocr.js <image-path-or-url> [--options]

Parameter Descriptions:

Parameter	Type	Default	Description
<image>	Required	—	Local path or HTTPS URL
--lang	string	eng	Language code(s), multiple joined with +, e.g., eng+chi_sim
--psm	number	—	Page segmentation mode (see PSM table below)
--oem	number	—	OCR engine mode (see OEM table below)
--whitelist	string	—	Character whitelist, e.g., 0123456789 to recognize only digits
--rectangle	string	—	Recognition region, format top,left,width,height
--output	string	text	Output format: text / hocr / blocks / tsv
--detect	flag	—	Detect text orientation and script (does not perform OCR)
--dpi	number	—	Manually specify image DPI

Common Examples:

# Basic mixed Chinese-English recognition
node scripts/ocr.js photo.jpg --lang chi_sim+eng

# Recognize digits only (license plates, CAPTCHAs, etc.)
node scripts/ocr.js captcha.png --whitelist 0123456789

# Column-based recognition (suitable for vertical Chinese text)
node scripts/ocr.js scroll.jpg --lang chi_sim --psm 4

# Specify a region for recognition
node scripts/ocr.js receipt.png --rectangle 50,100,400,200

# Detect image text orientation
node scripts/ocr.js rotated.jpg --detect

# Output structured data
node scripts/ocr.js doc.png --output blocks

# Manually specify DPI (avoids "Invalid resolution 0 dpi" warning)
node scripts/ocr.js scan.png --dpi 300

3. Batch Recognition of Multiple Images

To reuse a Worker, the AI should write an inline script:

const { createWorker } = require('tesseract.js');
(async () => {
  const worker = await createWorker('eng');
  for (const img of ['a.png', 'b.png', 'c.png']) {
    const { data: { text } } = await worker.recognize(img);
    console.log(img, '→', text);
  }
  await worker.terminate();
})();

---

PSM — Page Segmentation Modes

The --psm parameter controls how Tesseract analyzes page layout:

PSM	Name	Description
0	OSD_ONLY	Orientation and script detection only
1	AUTO_OSD	Automatic page segmentation + orientation detection
2	AUTO_ONLY	Automatic page segmentation, no orientation detection
3	AUTO	Fully automatic page segmentation (default)
4	SINGLE_COLUMN	Single column of variable size text
5	SINGLE_BLOCK_VERT_TEXT	Single block of vertical text
6	SINGLE_BLOCK	Single block of text
7	SINGLE_LINE	Single line of text
8	SINGLE_WORD	Single word
9	CIRCLE_WORD	Single word in a circular arrangement
10	SINGLE_CHAR	Single character
11	SPARSE_TEXT	Sparse text (find as much as possible)
12	SPARSE_TEXT_OSD	Sparse text + orientation detection
13	RAW_LINE	Raw line (treated as a single line)

OEM — OCR Engine Modes

OEM	Description
0	Legacy engine
1	LSTM neural network engine (default)
2	Legacy + LSTM
3	Default (automatically selected based on current configuration)

Language Code Quick Reference

Language	Code
English	eng
Simplified Chinese	chi_sim
Traditional Chinese	chi_tra
Japanese	jpn
Korean	kor
French	fra
German	deu
Spanish	spa
Russian	rus
Arabic	ara
Hindi	hin

Full list: tesseract_lang_list.md

Advanced Usage

The following scenarios require the AI to write inline scripts directly rather than using scripts/ocr.js:

• Reusing a Worker after switching languages: Use worker.reinitialize(langs, oem)
• Setting Tesseract parameters: Use worker.setParameters({ tessedit_pageseg_mode: ... })
• Detecting text orientation (requires Legacy engine): Call worker.detect(image) after createWorker('eng', 0, { legacyCore: true, legacyLang: true })
• Processing large numbers of images in parallel: Use createScheduler() + multiple Workers

For complete API reference, see references/api.md.