Resize Image Using PHP GD Library | PHP Tutorial For Beginners

Image resizing is an essential part of most web applications. To display uploaded images at a consistent size, you need to resize or crop them server-side. This tutorial uses PHP's built-in GD library to resize a JPEG image to a fixed 100×100 pixel thumbnail.

Before you begin: create an images/ folder (for the original upload) and a resize/ folder (for the output) in your project root.

Step 1 — HTML Upload Form

A simple form with enctype="multipart/form-data" to accept image files.

<html>
<head>
  <title>Resize image in PHP</title>
</head>
<body>
  <form name="form" action="<?php echo $_SERVER['PHP_SELF']; ?>"
        method="POST" enctype="multipart/form-data">
    <table>
      <tr>
        <td><label>Select image to resize:</label></td>
        <td><input type="file" name="file" id="file"></td>
      </tr>
      <tr>
        <td colspan="2">
          <input type="submit" value="Upload & Resize" name="submit">
        </td>
      </tr>
    </table>
  </form>
</body>
</html>

Step 2 — PHP Resize Code

When the form is submitted, PHP validates the file type and size, uploads the original to images/, then creates a resized copy in resize/ using GD.

<?php
if (isset($_POST['submit'])) {
    $error      = 0;
    $uploadfile = 'images/' . basename($_FILES['file']['name']);
    // $uploadfile — original image directory; can be unlinked after resizing
    $resize     = 'resize/';
    // $resize — destination directory for the resized image
    $file_name  = basename($_FILES['file']['name']);
    $filecheck  = basename($_FILES['file']['name']);
    $ext        = strtolower(substr($filecheck, strrpos($filecheck, '.') + 1));

    // Validate: only jpg/gif/png, max ~2 MB
    $allowed_ext  = ($ext == "jpg" || $ext == "gif" || $ext == "png");
    $allowed_type = ($_FILES["file"]["type"] == "image/jpeg"
                  || $_FILES["file"]["type"] == "image/gif"
                  || $_FILES["file"]["type"] == "image/png");
    $allowed_size = ($_FILES["file"]["size"] < 2120000);

    if (!($allowed_ext && $allowed_type && $allowed_size)) {
        echo "File Not Supported";
        $error = 1;
        die();
    }

    if ($_FILES['file']['name'] != "") {
        ini_set('memory_limit', '32M');

        if (!move_uploaded_file($_FILES['file']['tmp_name'], $uploadfile)) {
            echo "Error uploading file (check size limit).";
            $error = 1;
        } else {
            // Load original image and get its dimensions
            $img        = imagecreatefromjpeg($uploadfile);
            $width      = imagesx($img);
            $height     = imagesy($img);

            // Set target dimensions
            $new_width  = 100;
            $new_height = 100;

            // Create a blank canvas and copy the resized image onto it
            $tmp_img = imagecreatetruecolor($new_width, $new_height);
            imagecopyresized($tmp_img, $img, 0, 0, 0, 0,
                             $new_width, $new_height, $width, $height);

            // Save the resized image to the resize/ folder
            imagejpeg($tmp_img, "{$resize}{$file_name}");
        }
    }

    if ($error == 0) {
        echo "Image uploaded and resized successfully.";
        exit;
    }
}
?>

How It Works

imagecreatefromjpeg() — loads the uploaded JPEG into a GD image resource.
imagesx() / imagesy() — read the original width and height.
imagecreatetruecolor($new_width, $new_height) — creates a blank 100×100 canvas.
imagecopyresized() — copies and scales the original onto the new canvas.
imagejpeg($tmp_img, $path) — saves the result as a JPEG in the resize/ folder.

Hope this tutorial is useful for you. Keep following PHP Tutorial for Beginners for more help.