Deploy Object detection model using Flask

In this post, I am going to show you how you can deploy object detection model using Flask with Python. Now there are various ways to perform object detection in Python. To detect normal objects like persons, dogs, cats, etc. you can use pre-trained models like YOLO, Masked-RCNN, etc., or else if you want to detect custom objects like specific persons, fish, etc. you can train your own object detection model.

In this post, I will use YOLO model to build object detection Flask app. If you are new to Flask with Python, I recommend you to read the below articles before reading this post.

Also Read:

List down required functionalities

Before writing code, let’s first note down what kind of functionalities we need to achieve to build object detection using Flask.

  • We need a home page where we can upload any image files (input data for object detection)
  • Once the image is uploaded successfully, a message should show in green color. To do this we need to create a second home page
  • We need a button on the home page. If we click that button input image should display on the third page
  • On the third page (show image page), we need another button. If we click that button, the image with detected objects (object detection output) should display on the same page

Now let’s start writing codes to achieve the above functionalities. Let’s first write the homepage (index page), I am naming this file name as “index_upload_and_display_image.html


<!DOCTYPE html>
<html lang="en">
    <link rel="stylesheet" href='/staticFiles/main.css' />
    <h1>Flask GET, POST tutorial</h1>
    <p>Show CSV file in html using FLASK</p>

    <form method="POST" enctype="multipart/form-data" action="/">
        <input type="file" id="myFile" name="uploaded-file" accept=".jpg">
        <input type="submit" value="Submit">
  <p style="color:blue;">Choose csv file to upload</p>
  <form action="/show_data" target="_blank">
        <input type="submit" value="Show Image" />
Object detection web app using opencv and flask home page

Now if the input image is uploaded successfully a message should show in green color (“file uploaded successfully”). To do this we need to create a second home page. I am naming this page “index_upload_and_display_image_page2.html

Also Read:  Add HTML and CSS in Flask Web Application


<!DOCTYPE html>
<html lang="en">
    <link rel="stylesheet" href='/staticFiles/main.css' />
    <h1>Flask GET, POST tutorial</h1>
    <p>Show CSV file in html using FLASK</p>

    <form method="POST" enctype="multipart/form-data" action="/">
        <input type="file" id="myFile" name="uploaded-file" accept=".jpg">
        <input type="submit" value="Submit">
  <p style="color:green;">file uploaded successfully</p>
  <form action="/show_image" target="_blank">
        <input type="submit" value="Display Image" />
Object detection web app using opencv and flask and deeplearning home page

Please read the Upload and display image in Flask tutorial to better understand the above codes.

Now that we are done with two of our home pages, let’s now write our Flask back-end code. I am naming this code “

from flask import Flask, render_template, request, session, Response
import pandas as pd
from vaderSentiment.vaderSentiment import SentimentIntensityAnalyzer
from import json_normalize
import csv
import os
import cv2
import base64
import json
import pickle
from werkzeug.utils import secure_filename

import cv2
import numpy as np

#*** Backend operation

# WSGI Application
# Provide template folder name
# The default folder name should be "templates" else need to mention custom folder name

# Accepted image for to upload for object detection model
UPLOAD_FOLDER = os.path.join('staticFiles', 'uploads')
ALLOWED_EXTENSIONS = {'txt', 'pdf', 'png', 'jpg', 'jpeg', 'gif'}

app = Flask(__name__, template_folder='templateFiles', static_folder='staticFiles')

app.secret_key = 'You Will Never Guess'

# YOLO object detection function
def detect_object(uploaded_image_path):
    # Loading image
    img = cv2.imread(uploaded_image_path)

    # Load Yolo
    yolo_weight = "data/model/yolov3.weights"
    yolo_config = "data/model/yolov3.cfg"
    coco_labels = "data/model/coco.names"
    net = cv2.dnn.readNet(yolo_weight, yolo_config)

    classes = []
    with open(coco_labels, "r") as f:
        classes = [line.strip() for line in f.readlines()]

    # print(classes)

    # # Defining desired shape
    fWidth = 320
    fHeight = 320

    # Resize image in opencv
    img = cv2.resize(img, (fWidth, fHeight))

    height, width, channels = img.shape

    # Convert image to Blob
    blob = cv2.dnn.blobFromImage(img, 1 / 255, (fWidth, fHeight), (0, 0, 0), True, crop=False)
    # Set input for YOLO object detection

    # Find names of all layers
    layer_names = net.getLayerNames()
    # print(layer_names)
    # Find names of three output layers
    output_layers = [layer_names[i[0] - 1] for i in net.getUnconnectedOutLayers()]

    # Send blob data to forward pass
    outs = net.forward(output_layers)

    # Generating random color for all 80 classes
    colors = np.random.uniform(0, 255, size=(len(classes), 3))

    # Extract information on the screen
    class_ids = []
    confidences = []
    boxes = []
    for out in outs:
        for detection in out:
            # Extract score value
            scores = detection[5:]
            # Object id
            class_id = np.argmax(scores)
            # Confidence score for each object ID
            confidence = scores[class_id]
            # if confidence > 0.5 and class_id == 0:
            if confidence > 0.5:
                # Extract values to draw bounding box
                center_x = int(detection[0] * width)
                center_y = int(detection[1] * height)
                w = int(detection[2] * width)
                h = int(detection[3] * height)
                # Rectangle coordinates
                x = int(center_x - w / 2)
                y = int(center_y - h / 2)
                boxes.append([x, y, w, h])

    indexes = cv2.dnn.NMSBoxes(boxes, confidences, 0.5, 0.4)
    # Draw bounding box with text for each object
    font = cv2.FONT_HERSHEY_DUPLEX
    for i in range(len(boxes)):
        if i in indexes:
            x, y, w, h = boxes[i]
            label = str(classes[class_ids[i]])
            confidence_label = int(confidences[i] * 100)
            color = colors[i]
            cv2.rectangle(img, (x, y), (x + w, y + h), color, 2)
            cv2.putText(img, f'{label, confidence_label}', (x - 25, y + 75), font, 1, color, 2)

    # Write output image (object detection output)
    output_image_path = os.path.join(app.config['UPLOAD_FOLDER'], 'output_image.jpg')
    cv2.imwrite(output_image_path, img)


def index():
    return render_template('index_upload_and_display_image.html')

@app.route('/',  methods=("POST", "GET"))
def uploadFile():
    if request.method == 'POST':
        uploaded_img = request.files['uploaded-file']
        img_filename = secure_filename(uploaded_img.filename)['UPLOAD_FOLDER'], img_filename))

        session['uploaded_img_file_path'] = os.path.join(app.config['UPLOAD_FOLDER'], img_filename)

        return render_template('index_upload_and_display_image_page2.html')

def displayImage():
    img_file_path = session.get('uploaded_img_file_path', None)
    return render_template('show_image.html', user_image = img_file_path)

def detectObject():
    uploaded_image_path = session.get('uploaded_img_file_path', None)
    output_image_path = detect_object(uploaded_image_path)
    return render_template('show_image.html', user_image = output_image_path)

# flask clear browser cache (disable cache)
# Solve flask cache images issue
def add_header(response):
    response.headers["Cache-Control"] = "no-cache, no-store, must-revalidate"
    response.headers["Pragma"] = "no-cache"
    response.headers["Expires"] = "0"
    response.headers['Cache-Control'] = 'public, max-age=0'
    return response

if __name__=='__main__': = True)

Here in this code, in lines 31-120, I have written the YOLO object detection function, where the input of this function is an image and the output of this function is an image with a detected object marked with a bounding box and object name. The entire code I have borrowed from my previous post where I have explained YOLO object detection in detail.

In lines 152-158 (def add_header(response):) we are disabling the browser cache. If we are not doing this you may get errors like “flask image is not refreshing” or “flask image is not updating“.

Also Read:  Upload and Display CSV file in html table Flask Python

In lines 141 and 148 we are displaying input image and object detection output in the “show_image.html” file. So we need to write that code.


<!DOCTYPE html>
<html lang="en">
    <link rel="stylesheet" href='/staticFiles/main.css' />
    <h1>Object Detection Application using python and Flask</h1>
    <p>Detect object in image</p>

<img src="{{ user_image }}" alt="Italian Trulli" width="500" height="400">

  <form action="/detect_object" target="_blank">
        <input type="submit" value="Detect Object" />

Here in this code at line 10, we are calling image from Flask code.


Here in this post, I tried to give you a starting point to build and deploy object detection model using Flask. You can then modify it to develop your own project. In this post I used images but you can try to do real-time object detection using flask after reading this post. Both are similar, only you have to read the video, frame by frame and process frame by frame. You can read my previous post to understand how you can read and process images frame by frame to achieve real-time object detection for video or webcam.

If you have any questions or suggestions regarding this post, please let me know in the comment section below.

5 thoughts on “Deploy Object detection model using Flask”

  1. i want to detect yolov5 with video, then have the cropped of cell phone to go through cnn image classification to classify them as calculator or cell phone. I don’t know how to combine them


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