使用 IronOCR 處理 CAPTCHA

Curtis Chau

更新:2025年6月9日

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IronOCR 能否讀取驗證碼？

這雖有可能，但無法保證。

大多數 CAPTCHA 生成器都是刻意設計來迷惑 OCR 軟體的，有些甚至將"無法被 OCR 軟體讀取"（例如 Tesseract）作為單元測試的標準。

根據定義，驗證碼（Captcha）對 OCR 引擎而言極難辨識。圖像解析度極低，每個字元皆以特定角度排列，彼此間距各異，且背景包含不規則的雜訊。

去除背景雜訊的灰階圖像比彩色圖像更成功，但仍可能帶來挑戰：

OcrInput.DeNoise() 或 OcrInput.DeepCleanBackgroundNoise() 濾波器
OcrInput.ToGrayScale() 濾鏡

以下是一段 C# 範例程式碼，旨在透過去除雜訊並將 CAPTCHA 圖片轉為灰階，以提升 OCR 辨識效果：

using IronOcr;

class CaptchaReader
{
    static void Main(string[] args)
    {
        // Initialize the IronOCR engine
        var Ocr = new IronTesseract();

        // Create an OCR input object
        var Input = new OcrInput("captcha-image.jpg");

        // Apply noise reduction to improve OCR accuracy
        // This removes background noise while preserving text
        Input.DeNoise();

        // Optionally apply a deep clean for more aggressive noise removal
        Input.DeepCleanBackgroundNoise();

        // Convert the image to grayscale 
        // OCR works better on grayscale images compared to colored ones
        Input.ToGrayScale();

        // Perform OCR to extract text from the image
        var Result = Ocr.Read(Input);

        // Output the recognized text to the console
        Console.WriteLine(Result.Text);
    }
}

using IronOcr;

class CaptchaReader
{
    static void Main(string[] args)
    {
        // Initialize the IronOCR engine
        var Ocr = new IronTesseract();

        // Create an OCR input object
        var Input = new OcrInput("captcha-image.jpg");

        // Apply noise reduction to improve OCR accuracy
        // This removes background noise while preserving text
        Input.DeNoise();

        // Optionally apply a deep clean for more aggressive noise removal
        Input.DeepCleanBackgroundNoise();

        // Convert the image to grayscale 
        // OCR works better on grayscale images compared to colored ones
        Input.ToGrayScale();

        // Perform OCR to extract text from the image
        var Result = Ocr.Read(Input);

        // Output the recognized text to the console
        Console.WriteLine(Result.Text);
    }
}

Imports IronOcr

Friend Class CaptchaReader
	Shared Sub Main(ByVal args() As String)
		' Initialize the IronOCR engine
		Dim Ocr = New IronTesseract()

		' Create an OCR input object
		Dim Input = New OcrInput("captcha-image.jpg")

		' Apply noise reduction to improve OCR accuracy
		' This removes background noise while preserving text
		Input.DeNoise()

		' Optionally apply a deep clean for more aggressive noise removal
		Input.DeepCleanBackgroundNoise()

		' Convert the image to grayscale 
		' OCR works better on grayscale images compared to colored ones
		Input.ToGrayScale()

		' Perform OCR to extract text from the image
		Dim Result = Ocr.Read(Input)

		' Output the recognized text to the console
		Console.WriteLine(Result.Text)
	End Sub
End Class

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