Tesseract OCR Image Text Extraction#

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)

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Workflow#

1. Confirm Environment#

shell

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

If not installed:

shell

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

2. Execute Recognition#

Basic command:

shell

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

Parameter Descriptions:

ParameterTypeDefaultDescription<image>Required—Local path or HTTPS URL--langstringengLanguage code(s), multiple joined with +, e.g., eng+chi_sim``--psmnumber—Page segmentation mode (see PSM table below)--oemnumber—OCR engine mode (see OEM table below)--whiteliststring—Character whitelist, e.g., 0123456789 to recognize only digits--rectanglestring—Recognition region, format top,left,width,height``--outputstringtextOutput format: text / hocr / blocks / tsv``--detectflag—Detect text orientation and script (does not perform OCR)--dpinumber—Manually specify image DPI

Common Examples:

shell

# 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:

javascript

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();
})();

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PSM — Page Segmentation Modes#

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

PSMNameDescription0OSD_ONLYOrientation and script detection only1AUTO_OSDAutomatic page segmentation + orientation detection2AUTO_ONLYAutomatic page segmentation, no orientation detection3AUTOFully automatic page segmentation (default)4SINGLE_COLUMNSingle column of variable size text5SINGLE_BLOCK_VERT_TEXTSingle block of vertical text6SINGLE_BLOCKSingle block of text7SINGLE_LINESingle line of text8SINGLE_WORDSingle word9CIRCLE_WORDSingle word in a circular arrangement10SINGLE_CHARSingle character11SPARSE_TEXTSparse text (find as much as possible)12SPARSE_TEXT_OSDSparse text + orientation detection13RAW_LINERaw line (treated as a single line)

OEM — OCR Engine Modes#

OEMDescription0Legacy engine1LSTM neural network engine (default)2Legacy + LSTM3Default (automatically selected based on current configuration)

Language Code Quick Reference#

LanguageCodeEnglishengSimplified Chinesechi_simTraditional Chinesechi_traJapanesejpnKoreankorFrenchfraGermandeuSpanishspaRussianrusArabicaraHindihin

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.