How to detect and calculate the angle of an object inside a python image?

Question

I’m trying to write a code that detects lines and calculates an angle within a binary image (not necessarily this one, but always a similar spray). I read a few things about Hough Transform and even Scalar Product, but I can’t apply them.

For now I have this code only:

import cv2 
import numpy as np  
import math
import matplotlib.pyplot as plt

img_grey = cv2.imread('sprayang.jpg', cv2.IMREAD_GRAYSCALE)
img = cv2.GaussianBlur (img_grey, (5,5), 0)

th = 0
max_val = 255

    ret, o1 = cv2.threshold(img, th, max_val, cv2.THRESH_BINARY + cv2.THRESH_OTSU )

That gives me that image:

Using the Imagej angle tool, in this image, I read 90°.