首先，将错误的信息存储到数据库中，存储的是文件大小，而不是编码的图像。

$file_temp = base64_encode( file_get_contents( $_FILES['image']['tmp_name'] ) ); 
$image_size = getimagesize($file_temp);
$query = "INSERT INTO  questions(question_name, image, answer, category_id,level_id)
                        VALUES('$question', '$file_temp','$answer', '$category_id', '$level_id')";
$result = mysqli_query($conn, $query);
header("Location: display_question.php");

其次，如果已将文件的base64编码版本存储到数据库中，则在从数据库检索文件时不需要再次对其进行编码，以便 <img> 标签应该是

<?php echo "<img src='data:image/png;base64,$row[image]'/>"?>
</br><br/></td>

第三，也是最重要的一点，您需要使用参数化绑定查询来保护您的应用程序免受sql注入攻击

$file_temp = base64_encode( file_get_contents( $_FILES['image']['tmp_name'] ) ); 
$image_size = getimagesize($file_temp);
$query = "INSERT INTO  questions
                      (question_name, image, answer, category_id,level_id)
                VALUES(?,?,?,?,?)";

$stmt = $conn->prepare($query);
$stmt->bind_params('sssss',  $question, 
                            $file_temp,
                            $answer,
                            $category_id,
                            $level_id);
$result = $stmt->execute();
if (!$result) {
    echo $conn->error;
}
header("Location: display_question.php");

下面是将图片上传到特定文件夹的功能。您可以使用以下功能：

Param 1: is the folder where we need to store the new image  
Param 2: is FILES  
Param 3: if any prefix for the image we need to pass it.  
Param 4: if there is any previously uploaded image for same record. It should be deleted from the folder. Generally it is usefull when you are editing particluar record.  

uploadfile("profile",$_FILES,"profile_pic");

代码如下：

function uploadfile($folder,$data,$preFix = "logo_",$previousImage="") {
        $location = (pathinfo($_SERVER['SCRIPT_FILENAME']));
        $uploads_dir = $location['dirname'] . "/assets/uploads/" . $folder . "/";
        $fileNames = "";
        $tmp_name = $data["tmp_name"];
        $name = $data["name"];
        $fileExtension = pathinfo($name, PATHINFO_EXTENSION);
        $newfilename = $preFix . date("ymdhms") . '.' . $fileExtension;
        $fulldest = $uploads_dir . $newfilename;
        if (move_uploaded_file($tmp_name, $fulldest)) {
            if($previousImage != "")
                $this->removePreviousImage($folder, $previousImage);     //deleting existing image
            return $newfilename;
        } else {
            exit("Error File Uploading");
        }
    }