OCR Server

OCR Server is a simple stand-alone RESTful API for converting images of typed, handwritten or printed text into plain text, powered by Tesseract open source OCR engine.

Preperation of Tesseract

Get the language files of Tesseract from https://github.com/tesseract-ocr/tessdata. Make sure the TESSDATA_PREFIX environment variable is set to your tessdata directory.

Configuration File

The server settings can be specified using an optional JSON file named ocrServer.config.json. All fields are optional.

{
  // The IP address or host name of the server to listen to
  "hostname": "localhost",
  
  // The port number of the server to listen to
  "port": 8080,
  
  // Path to the file containing the SSL certificate (PEM format)
  "ssl_certificate": "cert.pem",
  
  // Path to the file containing the SSL private key (PEM format)
  "ssl_private_key": "key.pem",
  
  // An array of authorized API keys
  // Do not specify any API key to allow anonymous access
  "api_keys": [
    "Key 1",								        
    "Key 2"
  ]
}

Command Line Options

The command line options will overwrite the settings specified by the configuration file. The following command line options are available:

Option	Argument	Default	Description
--help			Displays the list of command line options
-h, --hostname	Name or IP	0.0.0.0	The IP address or host name of the server to listen to
-p, --port	Port Number	8080	The port number of the server to listen to
-c, --sslcert	File Path		Path to the file containing the SSL certificate (PEM format)
-p, --sslkey	File Path		Path to the file containing the SSL private key (PEM format)
-a, --apikey	API Key		The authorized API key, multiple keys are allowed

API Endpoints

• GET /ocr/languages Returns the sorted list of available Tesseract languages.

• POST /ocr/{LANGUAGE} Extracts and returns text from a given image in the specified language.

  • LANGUAGE: one of the available Tesseract languages (case sensitive)
  • Content-Type Header: an image mime type (image/png, image/gif, image/bmp, image/jpeg, image/tiff, or image/webp)
  • Request Body: the image as binary

If the server setting contains any API key, the API calls must be authorized. To do so, use the Authorization header and APIKEY authentication scheme to pass an API key to the server. For example, if 1234 is defined as an API key, the following HTTP header should be present in any request:

Authorization: APIKEY 1234