123step-green-verification.java

// 1 - read text from file
File file = new File("C://temp/green-pass.jpg");
BufferedImage bufferedImage = ImageIO.read(file);
LuminanceSource source = new BufferedImageLuminanceSource(bufferedImage);
BinaryBitmap bitmap = new BinaryBitmap(new HybridBinarizer(source));
Result result = new MultiFormatReader().decode(bitmap);
String text = result.getText();

// 2 - remove prefix "HC1:" and decode base45 string
byte[] bytecompressed = Base45.getDecoder().decode(text.substring(4));

// 3 - inflate string using zlib
Inflater inflater = new Inflater();
inflater.setInput(bytecompressed);
ByteArrayOutputStream outputStream = new ByteArrayOutputStream(bytecompressed.length);
byte[] buffer = new byte[BUFFER_SIZE];
while (!inflater.finished()) {
   final int count = inflater.inflate(buffer);
   outputStream.write(buffer, 0, count);
}

Related to medium article
https://gae-piaz.medium.com/green-pass-qr-code-signature-verification-java-f742079cc88