With PHP’s built in access to the decent GD graphics library, generating a thumbnail image from a larger photo turns out to be pretty simple to achieve. Below is a function you can use to create a thumbnail image from either a JPG, PNG or GIF source image.

To use, simply supply the file path to the source image as well as the desired width (though if not given it will be defaulted to 180 pixels wide). The height of the thumbnail is automatically generated so as to keep aspect ration the same.

The function is question:

function createThumbnail($pathToImage, $thumbWidth = 180) {
    $result = 'Failed';
    if (is_file($pathToImage)) {
        $info = pathinfo($pathToImage);

        $extension = strtolower($info['extension']);
        if (in_array($extension, array('jpg', 'jpeg', 'png', 'gif'))) {

            switch ($extension) {
                case 'jpg':
                    $img = imagecreatefromjpeg("{$pathToImage}");
                    break;
                case 'jpeg':
                    $img = imagecreatefromjpeg("{$pathToImage}");
                    break;
                case 'png':
                    $img = imagecreatefrompng("{$pathToImage}");
                    break;
                case 'gif':
                    $img = imagecreatefromgif("{$pathToImage}");
                    break;
                default:
                    $img = imagecreatefromjpeg("{$pathToImage}");
            }
            // load image and get image size

            $width = imagesx($img);
            $height = imagesy($img);

            // calculate thumbnail size
            $new_width = $thumbWidth;
            $new_height = floor($height * ( $thumbWidth / $width ));

            // create a new temporary image
            $tmp_img = imagecreatetruecolor($new_width, $new_height);

            // copy and resize old image into new image
            imagecopyresized($tmp_img, $img, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
                $pathToImage = $pathToImage . '.thumb.' . $extension;
            // save thumbnail into a file
            imagejpeg($tmp_img, "{$pathToImage}");
            $result = $pathToImage;
        } else {
            $result = 'Failed|Not an accepted image type (JPG, PNG, GIF).';
        }
    } else {
        $result = 'Failed|Image file does not exist.';
    }
    return $result;
}

//calling the function
$result = explode('|',createThumbnail($sourceImagePath, 180));
            if ($result[0] != 'Failed'){
                header('Location: /thumbnails/' . basename($result[0]));
            } else {
                header('Location: error.gif');
            }

As you can see, the function above returns a string, with the string containing ‘Failed’ if the thumbnail generation has failed for some reason, otherwise returning the path to the generated thumbnail image.

Nifty.