you must have to put your images in media folder and est full path please check below code i changed.

<?php
require_once 'app/Mage.php';
Mage::app();
Mage::app()->getStore()->setId(Mage_Core_Model_App::ADMIN_STORE_ID);
$importDir = Mage::getBaseDir('media') . DS . 'bulkimages/101/';

$productsData = array('Purple-Crown-Ring-MFAS.jpg','Purple-Crown-Ring-MFC.jpg','Purple-Crown-Ring-MSAS.jpg','Purple-Crown-Ring-MSF.jpg');

$productSKU = '111';
$ourProduct = Mage::getModel('catalog/product')->loadByAttribute('sku',$productSKU);

foreach($productsData as $fileName){
    $filePath = $importDir.$fileName;
    if (file_exists($filePath)) {
        $ourProduct->addImageToMediaGallery($filePath, array('image', 'small_image', 'thumbnail'), false, false);
        $ourProduct->save();
        echo "done ";
    } else {
        echo $productSKU . " not done";
        echo "<br>";
    }   
}
?>

You must have to put your images in media folder and est full path. Please check the below code i changed.

<?php
require_once 'app/Mage.php';
Mage::app();
Mage::app()->getStore()->setId(Mage_Core_Model_App::ADMIN_STORE_ID);
$importDir = Mage::getBaseDir('media') . DS . 'bulkimages/101/';

$productsData = array('Purple-Crown-Ring-MFAS.jpg','Purple-Crown-Ring-MFC.jpg','Purple-Crown-Ring-MSAS.jpg','Purple-Crown-Ring-MSF.jpg');

$productSKU = '111';
$ourProduct = Mage::getModel('catalog/product')->loadByAttribute('sku',$productSKU);

foreach($productsData as $fileName){
    $filePath = $importDir.$fileName;
    if (file_exists($filePath)) {
        $ourProduct->addImageToMediaGallery($filePath, array('image', 'small_image', 'thumbnail'), false, false);
        $ourProduct->save();
        echo "done ";
    } else {
        echo $productSKU . " not done";
        echo "<br>";
    }   
}
?>

  you must have to put your images in media folder and est full path please check below code i changed.

<?php
require_once 'app/Mage.php';
Mage::app();
Mage::app()->getStore()->setId(Mage_Core_Model_App::ADMIN_STORE_ID);
$importDir = Mage::getBaseDir('media') . DS . 'bulkimages/101/';

$productsData = array('Purple-Crown-Ring-MFAS.jpg','Purple-Crown-Ring-MFC.jpg','Purple-Crown-Ring-MSAS.jpg','Purple-Crown-Ring-MSF.jpg');

foreach($productsData as $fileName){
    $productSKU = '111';
    $ourProduct = Mage::getModel('catalog/product')->loadByAttribute('sku',$productSKU);
    $filePath = $importDir.$fileName;
    if (file_exists($filePath)) {
        $ourProduct->addImageToMediaGallery($filePath, array('image', 'small_image', 'thumbnail'), false, false);
        $ourProduct->save();
        echo "done ";
    } else {
        echo $productSKU . " not done";
        echo "<br>";
    }   
}
?>

  you must have to put your images in media folder and est full path please check below code i changed.

<?php
require_once 'app/Mage.php';
Mage::app();
Mage::app()->getStore()->setId(Mage_Core_Model_App::ADMIN_STORE_ID);
$importDir = Mage::getBaseDir('media') . DS . 'bulkimages/101/';

$productsData = array('Purple-Crown-Ring-MFAS.jpg','Purple-Crown-Ring-MFC.jpg','Purple-Crown-Ring-MSAS.jpg','Purple-Crown-Ring-MSF.jpg');

$productSKU = '111';
$ourProduct = Mage::getModel('catalog/product')->loadByAttribute('sku',$productSKU);

foreach($productsData as $fileName){
    $filePath = $importDir.$fileName;
    if (file_exists($filePath)) {
        $ourProduct->addImageToMediaGallery($filePath, array('image', 'small_image', 'thumbnail'), false, false);
        $ourProduct->save();
        echo "done ";
    } else {
        echo $productSKU . " not done";
        echo "<br>";
    }   
}
?>