What common error message might occur when trying to access images from a MySQL database in PHP?

When trying to access images from a MySQL database in PHP, a common error message that might occur is "Warning: Cannot modify header information - headers already sent by". This error typically happens when there is whitespace or other output before the header() function is called to display the image. To solve this issue, make sure there is no whitespace or any other output (such as echo or print statements) before calling the header() function to display the image.

<?php
// Connect to MySQL database
$conn = new mysqli("localhost", "username", "password", "database");

// Retrieve image data from database
$query = "SELECT image_data FROM images WHERE id = 1";
$result = $conn->query($query);
$row = $result->fetch_assoc();

// Set the appropriate header for image display
header("Content-type: image/jpeg");

// Display the image
echo $row['image_data'];