Image-Uploading表单给出错误代码2.为什么？

I am making a signup form for my new website. In the image uploading part of my form, the image doesn't seem to upload without any reason. I have seen everything twice and thrice still $_FILES['dp']['error'] is set to 2.

The file which I am trying to upload is of only 123 kb and it still keeps on showing error 2 and does not get uploaded. Why?

My HTML:

<form enctype="multipart/form-data" class="form-signin" role="form" method="post" action="addit.php">
<h2 class="form-signin-heading" align="center">Sign Up</h2>
<input value="" name="dp" type="file" class="form-control">
<button class="btn btn-lg btn-primary btn-block" type="submit">Sign up</button>

PHP:

$target_dir = "img/";

$target_file = $target_dir . basename($_FILES["dp"]["name"]);
echo $target_file;
echo $_FILES["dp"]["tmp_name"];
$uploadOk = 1;
$imageFileType = pathinfo($target_file,PATHINFO_EXTENSION);
// Check if image file is a actual image or fake image
// Check if file already exists
if (file_exists($target_file)) {
echo "Sorry, file already exists.";
$uploadOk = 0;
}
// Check file size
// Allow certain file formats
if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType != "jpeg"
&& $imageFileType != "gif" ) {
  echo "Sorry, only JPG, JPEG, PNG & GIF files are allowed.";
$uploadOk = 0;
}
// Check if $uploadOk is set to 0 by an error
if ($uploadOk == 0) {
echo "Sorry, your file was not uploaded.";
// if everything is ok, try to upload file
} else {
if (move_uploaded_file($_FILES["dp"]["tmp_name"], $target_file)) {
    echo "The file ". basename( $_FILES["dp"]["name"]). " has been  uploaded.";
} else {
    echo $_FILES['dp']['error'];
}
}

php.ini configurations:

file_uploads = On

; Temporary directory for HTTP uploaded files (will use system default if not
; specified).
; http://php.net/upload-tmp-dir
upload_tmp_dir = "d:/wamp/tmp"

; Maximum allowed size for uploaded files.
; http://php.net/upload-max-filesize
upload_max_filesize = 64M

; Maximum number of files that can be uploaded via a single request
max_file_uploads = 20

Use the code for your reference

$imgname = basename($_FILES["fileToUpload"]["name"]);
$target_dir = "../../images/";
$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
$uploadOk = 1;
$imageFileType = pathinfo($target_file,PATHINFO_EXTENSION);
// Check if image file is a actual image or fake image
if(isset($_POST["submit"])) {
    $check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
    if($check !== false) {
        echo "</br>File is an image - " . $check["mime"] . ".";
        $uploadOk = 1;
    } else {
        echo "</br>File is not an image.";
        $uploadOk = 0;
    }
}
// Check if file already exists
if (file_exists($target_file)) {
    echo "</br>Sorry, file already exists.";
    $uploadOk = 0;
}
// Check file size
if ($_FILES["fileToUpload"]["size"] > 500000) {
    echo "</br>Sorry, your file is too large.";
    $uploadOk = 0;
}
// Allow certain file formats
if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType != "jpeg"
&& $imageFileType != "gif" ) {
    echo "</br>Sorry, only JPG, JPEG, PNG & GIF files are allowed.";
    $uploadOk = 0;
}
// Check if $uploadOk is set to 0 by an error
if ($uploadOk == 0) {
    echo "</br>Sorry, your file was not uploaded.";
// if everything is ok, try to upload file
} else {
    if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $target_file)) {
        echo "</br>The file ". basename( $_FILES["fileToUpload"]["name"]). " has been uploaded.";
    } else {
        echo "</br>Sorry, there was an error uploading your file.";
    }
}