Subida

<?php
error_reporting(E_ALL);
ini_set("display_errors", "1");

if (isset($_FILES["file"])) {
    $fileExtensions = explode($_POST["extensions"]);
    $file = $_FILES["file"];
    $uploadFileDir = $_POST["folder"];
    if (isset($file) && $file["error"] === UPLOAD_ERR_OK) {
        $fileTmpPath = $file["tmp_name"];
        $fileName = $file["name"];
        $fileSize = $file["size"];
        $fileType = $file["type"];
        $fileNameCmps = explode(".", $fileName);
        $fileName = empty($_POST["name"]) ? reset($fileNameCmps) : $_POST["name"];
        $fileExtension = strtolower(end($fileNameCmps));

        if (in_array($fileExtension, $fileExtensions)) {
            $dest_path = "{$uploadFileDir}{$fileName}.{$fileExtension}";
            if (move_uploaded_file($fileTmpPath, $dest_path))
                echo "OK";
            else
                echo "NO";
        } else
            echo "NO EXT";
    } else
        echo "ERR";
}
?>
<form action="" method="post" enctype="multipart/form-data">
    <input type="hidden" name="extensions" value="jpg,gif,png">
    <input type="hidden" name="folder" value="">
    <div>
        <label>Nombre - opcional</label>
        <input type="text" name="name">
    </div>
    <div>
        <label>Archivo</label>
        <input oninvalid="this.setCustomValidity('No sea boludo, tiene que subir una imagen" oninput="setCustomValidity('')" required type="file" name="file">
    </div>
    <button type="submit">cargar</button>
</form>