from PyQt5.QtGui import *
from PyQt5.QtCore import *
from PyQt5.QtWidgets import *
import sys

class Labella(QLabel):
    def __init__(self, parent):
        super().__init__(parent=parent)
        self.flag = False
        pixmap = QPixmap('images.jpg')
        self.setPixmap(pixmap)
        self.resize(pixmap.width(), pixmap.height())

    def paintEvent(self, e):
        if self.flag:
            q = QPainter()  # Painting the line

            q.begin(self)

            q.drawRect(self.firstX, self.firstY, self.x - self.firstX, self.y - self.firstY)

            q.end()
            self.update()

    def mousePressEvent(self, e):
        self.flag = True
        self.firstX = e.x()
        self.firstY = e.y()

    def mouseMoveEvent(self, e):
        self.x = e.x()
        self.y = e.y()


class MouseTracker(QMainWindow):
    distance_from_center = 0
    def __init__(self):
        super().__init__()
        self.test = 0
        self.x = -1
        self.y = -1
        self.firstX = -1
        self.firstY = -1
        self.initUI()


    def initUI(self):
        self.setGeometry(200, 200, 1000, 500)
        self.setWindowTitle('Mouse Tracker')

        lbl = Labella(self)

        self.show()

    def mousePressEvent(self, e):
        self.firstX = e.x()
        self.firstY = e.y()

    def mouseMoveEvent(self, event):
        self.x = event.x()
        self.y = event.y()

        self.update()

    def paintEvent(self, e):
        if not (self.firstX == -1 or self.firstY == -1):
            q = QPainter()  # Painting the line

            q.begin(self)

            q.drawRect(self.firstX, self.firstY, abs(self.x - self.firstX), abs(self.y - self.firstY))

            q.end()


app = QApplication(sys.argv)
ex = MouseTracker()
sys.exit(app.exec_())

from PyQt5.QtGui import *
from PyQt5.QtCore import *
from PyQt5.QtWidgets import *


class Labella(QLabel):
    def __init__(self):
        super().__init__()
        self.flag = False

        pixmap = QPixmap('images.jpg')
        self.setPixmap(pixmap)
        self.resize(pixmap.size())

        self.x = 0
        self.y = 0
        self.firstX = 0
        self.firstY = 0

    def paintEvent(self, e):
        super().paintEvent(e)

        if self.flag:
            painter = QPainter(self)

            painter.setPen(Qt.red)
            painter.setBrush(Qt.red)

            painter.drawRect(self.firstX, self.firstY, self.x - self.firstX, self.y - self.firstY)

    def mousePressEvent(self, e):
        self.flag = True
        self.firstX = e.x()
        self.firstY = e.y()

    def mouseReleaseEvent(self, e):
        self.flag = False

    def mouseMoveEvent(self, e):
        self.x = e.x()
        self.y = e.y()

        self.update()


if __name__ == '__main__':
    app = QApplication([])

    mw = Labella()
    mw.show()

    app.exec()