Opencv bounding box issue

Hi, I’m still learning machine vision, so any assistance is welcomed.

I have an image I need to draw a bounding box around and I’m trying to use the code at bottom of this post. The issue I have is that I have tried to blur the blue box shape to remove its details e.g.


but the blurred image doesnt seem to have a good enough edge to produce a bounding box.

I have found that if I use my code below with a plain blue square with sharp edges of the same size as the shipping container shown in the image below, it works just fine. It seems the detail within the blue area stops a boundary box being drawn.

Any help appreciated.

Opencv is v4.6.0.66 on windows 10

import cv2

img = cv2.imread('blue_object.jpg')

gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

edged = cv2.Canny(img, 120,890)

thresh = cv2.adaptiveThreshold(edged, 255, 1, 1, 11, 2)
thresh_color = cv2.cvtColor(thresh, cv2.COLOR_GRAY2BGR)

thresh = cv2.dilate(thresh,None,iterations = 50)
thresh = cv2.erode(thresh,None,iterations = 50)

contours,hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

for cnt in contours:
    area = cv2.contourArea(cnt)
    if area > 50000:
        x,y,w,h = cv2.boundingRect(cnt)