如何替换php中的现有图像？

<?php
// 检查是否有文件上传
if (isset($_FILES['image'])) {
    $file = $_FILES['image'];
    $imageFileType = strtolower(pathinfo($file['name'], PATHINFO_EXTENSION));

    // 检查文件是否为允许的图像类型
    $check = getimagesize($file["tmp_name"]);
    if ($check !== false) {
        // 删除旧图像
        if (file_exists('old_image.jpg')) {
            unlink('old_image.jpg');
        }

        // 移动上传的文件到目标目录
        if (move_uploaded_file($file["tmp_name"], "new_image.jpg")) {
            echo "The file ". htmlspecialchars( basename( $file["name"])). " has been uploaded.";
        } else {
            echo "Sorry, there was an error uploading your file.";
        }
    } else {
        echo "File is not an image.";
    }
}
?>

<!-- HTML 表单 -->
<form action="upload_image.php" method="post" enctype="multipart/form-data">
    Select image to upload:
    <input type="file" name="image">
    <input type="submit" value="Upload Image" name="submit">
</form>