File Upload code in PHP with few validations

fileUpload.php

<?php

$target_dir = "photos/";
$target_file = $target_dir . basename($_FILES["photo"]["name"]);
$uploadOk = 1;
$imageFileType = strtolower(pathinfo($target_file, PATHINFO_EXTENSION));
// Check if image file is a actual image or fake image
if (isset($_POST["submit"])) {
    $check = getimagesize($_FILES["photo"]["tmp_name"]);
    if ($check !== false) {
        echo "File is an image - " . $check["mime"] . ".";
        $uploadOk = 1;
    } else {
        echo "File is not an image.";
        $uploadOk = 0;
    }
}
// Check if file already exists
if (file_exists($target_file)) {
    echo "Sorry, file already exists.";
    //$uploadOk = 0;
    $uploadOk = 1;
}
// Check file size
if ($_FILES["photo"]["size"] > 500000) {
    echo "Sorry, your file is too large.";
    $uploadOk = 0;
}
// Allow certain file formats
if ($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["photo"]["tmp_name"], "../" . $target_file)) {
        echo "The file " . basename($_FILES["photo"]["name"]) . " has been uploaded.";
    } else {
        $error = "Sorry, there was an error uploading your file.";
    }
}
?>