How to modify multiple pictures from folder using opencv in c++ (OpenCV, VS2019,Cmake,C++)

Question

I'm trying to modify this code I found here for my Thesis : https://github.com/carolinepacheco/lbp-library, so that it creates a new directory in C:, and there stores the modified pictures I loaded. Problem is, that I can only get the new directory created, but have yet to make the code load all the pictures from a folder I got on my desktop (DRIVE Retinal Dataset - "C:\Users\Vassilis\Desktop\DriveFinal\*.TIF"), and then modify them. I'm uploading the code too, and hope for your support...

#include <opencv2/opencv.hpp>

#include <vector>
#include <String>
#include <conio.h>
#include <stdio.h>
#include <stdlib.h>
#include <direct.h>

#include "lbplibrary.hpp"
using namespace lbplibrary;
using namespace std;
stringstream ss;




void makedir()
{

    if (_mkdir("\\drivemodded") == 0)
    {
        printf("Directory '\\drivemodded' was successfully created, lbp images can now be stored\n");
        system("dir \\drivemodded");

    }
    else
        printf("Problem creating directory '\\drivemodded', maybe it already exists...\n");

}


void test_image()
{
    String folder = "C:\\Users\\Vassilis\\Desktop\\DriveFinal\\*.TIF";
    vector<cv::String> filenames;
    cv::Mat img_output;
    cv::Mat img_input;
    cv::Mat ct; //mhpws = 0 ???

    cv::glob(folder, filenames);


    //cv::Mat img_input = cv::imread("frames/1.png");

    for (size_t i = 0; i < filenames.size(); i++)
    {
        cv::Mat img_input = cv::imread(filenames[i]);


        cv::imshow("Input", img_input);

        cv::cvtColor(img_input, img_input, cv::COLOR_BGR2GRAY);
        //cv::GaussianBlur(img_input, img_input, cv::Size(7, 7), 5, 3, cv::BORDER_CONSTANT);

        LBP* lbp;
        lbp = new OLBP;     // 0-255
        //lbp = new ELBP;     // 0-255
        //lbp = new VARLBP;   // 0-953.0
        //lbp = new CSLBP;    // 0-15
        //lbp = new CSLDP;    // 0-15
        //lbp = new XCSLBP;   // 0-15
        //lbp = new SILTP;    // 0-80
        //lbp = new CSSILTP;  // 33-120
        //lbp = new SCSLBP;   // 0-15
        //lbp = new BGLBP;    // 0-239
        lbp->run(img_input, img_output);

        double min, max; cv::minMaxLoc(img_output, &min, &max); std::cout << "min: " << min << ", max: " << max;
        cv::normalize(img_output, img_output, 0, 255, cv::NORM_MINMAX, CV_8UC1);




        cv::imshow("Output", img_output);


        

        cv::imwrite("C:\\drivemodded", img_output);
    }
    cv::waitKey(0);
    
}


int main(int argc, const char** argv)
{
    makedir();


    test_image();
    

    return 0;
}