QR Code Attendance System

Abstract

QR codes turn any phone or printout into a scannable ID — which is why they run everything from event check-ins to classroom attendance. This project wires together two libraries: qrcode to generate a code for each user, and OpenCV to scan it through a webcam and stamp the time. You’ll build the generate-and-scan core, then turn the toy into a usable system: a database of records, duplicate-scan prevention, a live camera overlay that shows the decoded ID, and CSV export for reports.

You will leave understanding:

• How QR codes encode arbitrary text and how qrcode renders them.
• The OpenCV capture loop: open camera → read frame → detect → release.
• Why the naive version can’t tell who’s already checked in (and how to fix it).
• How to move from “popup says scanned” to a real attendance log.

Prerequisites

• Python 3.6 or above.
• A text editor or IDE.
• pip install qrcode[pil] opencv-python.
• A working webcam.
• Tkinter (bundled with Python).

Getting Started

Create the project

1. Create a folder named qr-attendance.
2. Inside it, create qr_code_attendance_system.py.
3. Install dependencies: pip install qrcode[pil] opencv-python.

Write the code

qr_code_attendance_system.py

pch.viewSource

qr_code_attendance_system.py

"""
QR Code Attendance System

A Python application that generates QR codes for users and scans them to mark attendance. Features include:
- Generating QR codes for user identification.
- Scanning QR codes to mark attendance.
"""

import qrcode
import cv2
from tkinter import Tk, Label, Entry, Button, messagebox
from datetime import datetime


class QRCodeAttendanceSystem:
    def __init__(self, root):
        self.root = root
        self.root.title("QR Code Attendance System")

        Label(root, text="Enter User ID:").grid(row=0, column=0, padx=10, pady=10)
        self.user_id_entry = Entry(root, width=30)
        self.user_id_entry.grid(row=0, column=1, padx=10, pady=10)

        Button(root, text="Generate QR Code", command=self.generate_qr_code).grid(row=1, column=0, columnspan=2, pady=10)
        Button(root, text="Scan QR Code", command=self.scan_qr_code).grid(row=2, column=0, columnspan=2, pady=10)

    def generate_qr_code(self):
        """Generate a QR code for the entered user ID."""
        user_id = self.user_id_entry.get()
        if not user_id:
            messagebox.showerror("Error", "Please enter a User ID.")
            return

        qr = qrcode.QRCode(version=1, box_size=10, border=5)
        qr.add_data(user_id)
        qr.make(fit=True)

        img = qr.make_image(fill="black", back_color="white")
        img_path = f"{user_id}_qr.png"
        img.save(img_path)

        messagebox.showinfo("Success", f"QR Code generated and saved as {img_path}.")

    def scan_qr_code(self):
        """Scan a QR code to mark attendance."""
        cap = cv2.VideoCapture(0)
        detector = cv2.QRCodeDetector()

        while True:
            ret, frame = cap.read()
            if not ret:
                break

            data, bbox, _ = detector.detectAndDecode(frame)
            if data:
                timestamp = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
                messagebox.showinfo("Attendance Marked", f"User ID: {data}\nTime: {timestamp}")
                break

            show_or_save("QR Code Scanner", frame)
            if wait_or_skip(1) & 0xFF == ord("q"):
                break

        cap.release()
        cv2.destroyAllWindows() if "--show" in __import__("sys").argv else None


def main():
    root = Tk()
    app = QRCodeAttendanceSystem(root)
    root.mainloop()


def wait_or_skip(delay=0):
    """cv2.waitKey needs a window; without one it raises. Skip it instead."""
    import sys

    if "--show" in sys.argv:
        return cv2.waitKey(delay)
    return -1


def show_or_save(title, image, _counter=[0]):
    """Display the frame, or write it to a file when no window is available.

    Headless OpenCV has no GUI at all, and even a full build cannot open a
    window over SSH or inside a container. Falling back to a file keeps the
    project runnable everywhere and leaves something to look at afterwards.
    """
    import os
    import re as _re

    if "--show" in __import__("sys").argv:
        cv2.imshow(title, image)
        return None
    _counter[0] += 1
    stem = _re.sub(r"\W+", "_", title).strip("_").lower() or "frame"
    name = f"{stem}.png" if _counter[0] == 1 else f"{stem}_{_counter[0]}.png"
    cv2.imwrite(name, image)
    print(f"saved {name}  ({os.path.getsize(name):,} bytes)")
    return name


if __name__ == "__main__":
    main()

Run it

command

C:\Users\Your Name\qr-attendance> python qr_code_attendance_system.py
# Enter a User ID and "Generate QR Code" -> saves <id>_qr.png
# "Scan QR Code" opens the webcam; show the code to mark attendance.

How it fits together

Read from the top: this is what runs when you execute the file, and which function calls which. It is generated from the code, so it cannot drift from it.

diagram Diagram mermaid

  flowchart TD
  RUN(["python qr_code_attendance_system.py"])
  QRCodeAttendanceSystem["QRCodeAttendanceSystem
class"]
  main("main")
  wait_or_skip("wait_or_skip")
  show_or_save("show_or_save")
  RUN --> main
  QRCodeAttendanceSystem --> show_or_save
  QRCodeAttendanceSystem --> wait_or_skip
  main --> QRCodeAttendanceSystem

Step-by-Step Explanation

1. Generating a QR code

qr_code_attendance_system.py

qr = qrcode.QRCode(version=1, box_size=10, border=5)
qr.add_data(user_id)
qr.make(fit=True)
img = qr.make_image(fill="black", back_color="white")
img.save(f"{user_id}_qr.png")

A QR code is just text encoded as a grid. version sets capacity (1 = smallest), box_size is pixels per module, border is the quiet zone around it. fit=True auto-grows the version if the data doesn’t fit. Here the encoded data is simply the user ID.

2. Opening the camera

qr_code_attendance_system.py

cap = cv2.VideoCapture(0)          # 0 = default webcam
detector = cv2.QRCodeDetector()

VideoCapture(0) grabs the first camera. QRCodeDetector is OpenCV’s built-in QR reader — no extra library needed.

3. The scan loop

qr_code_attendance_system.py

while True:
    ret, frame = cap.read()
    if not ret:
        break
    data, bbox, _ = detector.detectAndDecode(frame)
    if data:
        timestamp = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
        messagebox.showinfo("Attendance Marked", f"User ID: {data}\nTime: {timestamp}")
        break
    cv2.imshow("QR Code Scanner", frame)
    if cv2.waitKey(1) & 0xFF == ord("q"):
        break
cap.release()
cv2.destroyAllWindows()

Each loop reads a frame, tries to decode a QR code, and on success stamps the time and stops. cv2.imshow shows the live feed; waitKey(1) keeps it responsive and lets q quit. Always release() the camera and destroyAllWindows() — skip it and the webcam stays locked.

The Core Problem: Nothing Is Actually Stored

The naive version pops a message and forgets. A real system needs a record. Add SQLite:

db.py

import sqlite3
 
conn = sqlite3.connect("attendance.db")
conn.execute("""CREATE TABLE IF NOT EXISTS attendance (
    user_id TEXT, timestamp TEXT
)""")
 
def mark(user_id):
    ts = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
    conn.execute("INSERT INTO attendance VALUES (?, ?)", (user_id, ts))
    conn.commit()

Note ? placeholders — never f-string user input into SQL (injection risk).

Prevent Duplicate Scans

A code lingering in view marks attendance dozens of times. Check today’s log first:

dedupe.py

def already_marked_today(user_id):
    today = datetime.now().strftime("%Y-%m-%d")
    row = conn.execute(
        "SELECT 1 FROM attendance WHERE user_id=? AND timestamp LIKE ?",
        (user_id, f"{today}%")).fetchone()
    return row is not None

Mark only if not already_marked_today(data).

Draw a Live Overlay

Show the detected box and ID on the video so the user knows it worked:

overlay.py

if data and bbox is not None:
    pts = bbox.astype(int).reshape(-1, 2)
    for i in range(len(pts)):
        cv2.line(frame, tuple(pts[i]), tuple(pts[(i + 1) % len(pts)]), (0, 255, 0), 2)
    cv2.putText(frame, data, tuple(pts[0]), cv2.FONT_HERSHEY_SIMPLEX, 0.8, (0, 255, 0), 2)

Export to CSV

For reports, dump the table:

export.py

import csv
def export():
    rows = conn.execute("SELECT user_id, timestamp FROM attendance").fetchall()
    with open("attendance.csv", "w", newline="") as f:
        csv.writer(f).writerows([("User ID", "Time"), *rows])

Common Mistakes

Problem	Cause	Fix
Camera stays on / locked	Forgot release()	Always cap.release() + destroyAllWindows()
Same person marked many times	No duplicate check	Skip if already marked today
Attendance vanishes on exit	Nothing persisted	Store in SQLite/CSV
Black window, no feed	Wrong camera index or in-use	Try VideoCapture(1); close other apps
QR won’t scan	Too small / poor lighting / glare	Larger box_size, better light, hold steady
SQL breaks on odd IDs	String-formatted query	Use ? parameterized queries

Variations to Try

1. User registry — generate codes for a whole roster from a CSV.
2. Check-in / check-out — track both, compute hours present.
3. Web dashboard — live attendance via Flask (see Simple Blog with Flask).
4. Encrypted payloads — sign the QR data so codes can’t be forged.
5. Email/SMS confirmation — notify on successful check-in.
6. Photo capture — save a webcam snapshot with each scan.
7. Mobile scanning — a companion phone app posting to your API.

Real-World Applications

• Events & conferences — ticketed entry and session check-in.
• Schools & offices — class and workplace attendance.
• Gyms & memberships — access logging.
• Inventory & logistics — scanning items in and out.

Educational Value

• QR generation & decoding — encoding data, the qrcode and OpenCV APIs.
• Computer vision basics — the capture/detect/release loop.
• Database design — records, queries, and safe parameterization.
• Data integrity — duplicate prevention and exports.

Next Steps

• Persist scans to SQLite with duplicate prevention.
• Add a live overlay showing the decoded ID.
• Support check-in/check-out and CSV export.
• Generate codes for a whole roster at once.

Conclusion

You combined qrcode and OpenCV into a scan-to-log attendance system, then closed the gap that makes the naive version a toy: it now remembers, refuses duplicates, and exports reports. Generate-then-scan plus a database is the exact recipe behind ticketing, access control, and inventory systems everywhere. Full source on GitHub. Explore more computer-vision projects on Python Central Hub.