画面表示（ｽｸﾘｰﾝｼｮｯﾄ）から、QRｺｰﾄﾞを読み込んで、ﾃﾞｺｰﾄﾞする

C#の単体ｱﾌﾟﾘです

※同様の機能のﾌｫｰﾑｱﾌﾟﾘはこちら
https://qiita.com/santarou6/items/d1090338def65f3af5bc

screen_qr_decode.cs

//c:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe /reference:QRCodeEncoderDecoderLibrary.dll /target:winexe screen_qr_decode.cs

using System;
using System.Windows.Forms;
using System.Drawing;
using QRCodeEncoderDecoderLibrary;

public class screen_qr_decode
{
 public static void Main(string[] args)
 {
	try{
    QRDecoder	QRCodeDecoder;
    Bitmap		QRCodeInputImage;
    QRCodeDecoder = new QRDecoder();
    QRCodeInputImage = new Bitmap(Screen.PrimaryScreen.Bounds.Width,Screen.PrimaryScreen.Bounds.Height);

    Graphics g = Graphics.FromImage(QRCodeInputImage);
    g.CopyFromScreen(new Point(0, 0), new Point(0, 0), QRCodeInputImage.Size);
    g.Dispose();

    QRCodeInputImage.Save("temporary.png", System.Drawing.Imaging.ImageFormat.Png);
    
    byte[][] DataByteArray = QRCodeDecoder.ImageDecoder(QRCodeInputImage);
    
    //string Result = System.Text.Encoding.GetEncoding(932).GetString(DataByteArray[0]);
    string Result = System.Text.Encoding.UTF8.GetString(DataByteArray[0]);
    //string Result = System.Text.Encoding.GetEncoding(51932).GetString(DataByteArray[0]);
    
    MessageBox.Show(Result);

	}
	catch(Exception ex){
		MessageBox.Show("読み取りエラー\n\n"+ex);
	}

 }

}

実行例

※ライブラリは以下参照
QR Code Encoder and Decoder .NET Class Library
https://www.codeproject.com/Articles/1250071/QR-Code-Encoder-and-Decoder-NET-Class-Library-Writ

QRCodeEncoderDecoderLibrary.dll