The $_POST do not obtain the file, the correct is $_FILES and the form must have enctype="multipart/form-data", before leaving doing anything I recommend you start studying by the documentation https://secure.php.net/manual/en/features.file-upload.post-method.php.
A basic example should look something like this:
<html>
<body>
    <form action="" method="post" enctype="multipart/form-data">
        Selecione : <input name="arquivo" type="file">
        <input type="submit" value="Enviar">
    </form>
    <?php
    //Salva a foto com nome aleatório dentro da pasta
    $pasta = 'pasta-upload';
    $arq = $pasta . '/' . uniqid(rand(), true);
    $image = false;
    if (!chmod($pasta, 0755)) {
        echo 'Erro ao mudar as permissões';
    } else if (isset($_FILES['arquivo']['tmp_name'])) {
        if ($_FILES['arquivo']['error'] !== UPLOAD_ERR_OK) {
            echo 'Erro no upload';
        } else {
            $tmp = $_FILES['arquivo']['tmp_name'];
            $image = getimagesize($tmp);
            $ext = str_replace(array('image/', 'x-'), '', $image['mime']);
            $arq .= '.' . $ext;
            if (!$image) {
                echo 'Formato invalido';
            } else if (!move_uploaded_file($tmp, $arq)) {
                echo 'Erro ao mover o arquivo';
            } else {
                echo '<img src="', $arq, '">';
            }
        }
    }
    ?>
   </body>
</html>
- In the example use a folder called - pasta-upload, it must be in the same folder as index.php
 
- The - action=""this empty, this causes the upload to be sent to the same page
 
 
First, add
enctype="multipart/form-data"to the elementform. Second, your file will be available at$_FILES["arquivo"], not in$_POST. Third, try reading this material, I believe it will help you.– Woss
Show on index, okay, but which page is this upload? and which directory is?
– user60252
the image ta on the desktop
– Manuel Jose