qt and Opencv linking error "undefined reference"

I tried to set up opencv in qt and followed the steps exactly from here https://wiki.qt.io/How_to_setup_Qt_and_openCV_on_Windows, but got linking error like

"undefined reference to cv::imread(cv::String const&, int)' debug/mainwindow.o: In function MainWindow::MainWindow(QWidget*)': C:\Users\Han\Desktop\QT_projects\build-TEST_OPENCV-Desktop_Qt_5_15_2_MinGW_64_bit->Debug/../TEST_OPENCV/mainwindow.cpp:17: undefined reference to `cv::imread(cv::String const&, >int)'"

Here's the path of my opencv: C:\opencv-build\install\x86\mingw\lib

Things I tried: Using the "add library" on Qt. However, qt coudlnt find the file that I specified.

My code: .pro file

#-------------------------------------------------
#
# Project created by QtCreator 2017-03-05T12:30:06
#
#-------------------------------------------------

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = opencvtest
TEMPLATE = app

# The following define makes your compiler emit warnings if you use
# any feature of Qt which as been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0


SOURCES += main.cpp\
        mainwindow.cpp

HEADERS  += mainwindow.h

FORMS    += mainwindow.ui

INCLUDEPATH += C:\opencv\build\include

LIBS += C:\opencv-build\bin\libopencv_core343.dll
LIBS += C:\opencv-build\bin\libopencv_highgui343.dll
LIBS += C:\opencv-build\bin\libopencv_imgcodecs343.dll
LIBS += C:\opencv-build\bin\libopencv_imgproc343.dll
LIBS += C:\opencv-build\bin\libopencv_features2d343.dll
LIBS += C:\opencv-build\bin\libopencv_calib3d343.dll

# more correct variant, how set includepath and libs for mingw
# add system variable: OPENCV_SDK_DIR=D:/opencv/opencv-build/install
# read http://doc.qt.io/qt-5/qmake-variable-reference.html#libs

#INCLUDEPATH += $$(OPENCV_SDK_DIR)/include

#LIBS += -L$$(OPENCV_SDK_DIR)/x86/mingw/lib \
#        -lopencv_core320        \
#        -lopencv_highgui320     \
#        -lopencv_imgcodecs320   \
#        -lopencv_imgproc320     \
#        -lopencv_features2d320  \
#        -lopencv_calib3d320

main

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    // read an image
    cv::Mat image = cv::imread("f://1.jpg", 1);
    // create image window named "My Image"
    cv::namedWindow("My Image");
    // show the image on window
    cv::imshow("My Image", image);
}

MainWindow::~MainWindow()
{
    delete ui;
}

I appreciate any kind of help. Thanks!