Spring Check if an image has a qr code then scan it

Question

I am creating a application where if it is used on a phone you can take a picture of a qr code, it would then check if it had a qr code in the picture and if it did, it would check if this qr code was that I had saved in my "src/main/resources/qr_codes"

I'm not sure about how to go about doing this, I have currently got it so the image name is printed out in the controller by sending it to the controller. How would I go about and doing this. Everything on google points me towards Generating them but I've already created them on a website. This is the code I have so far.

    @RequestMapping(value="/qr")
public String qr_code(RedirectAttributes redA,HttpServletRequest req) {
    System.out.println(req.getParameter("qr")); //prints out image.jpg
    return "redirect:/home";
}

How would I then scan this image to check if it had a qr code and then check if it matched one of the qr codes that I created Thank you for your time. Jeff