Magento – Setting Product Images for Products not Displaying image

Here is given programmatically adding media images to product, you can adjust this code to your own importing script:

    $mediaGalleryAttribute = Mage::getModel('catalog/resource_eav_attribute')
        ->loadByCode(Mage_Catalog_Model_Product::ENTITY, 'media_gallery');
    $mediaGallery          = $mediaGalleryAttribute->getBackend();
    $attrCode              = $mediaGalleryAttribute->getAttributeCode();


    $product          = Mage::getModel('catalog/product')->load($productId);
    $mediaGalleryData = $product->getData($attrCode);
    /**
     * If you want to remove old images use this code
     */
    if (isset($mediaGalleryData['images'])) {
        foreach ($mediaGalleryData['images'] as &$image) {
            $image['removed'] = 1;
        }
        $product->setData($attrCode, $mediaGalleryData);
    }
    /**
     * Here is real image file path
     */
    $thumbnailFile = 'real/path/to/thumbnail/file.jpg';
    $imageFile     = 'real/path/to/image/file.jpg';
    try {
        //Set thumbnail
        $imageFileUri = $mediaGallery->addImage($product, $thumbnailFile, null, false, false);
        $mediaGallery->setMediaAttribute($product, 'thumbnail', $imageFileUri);

        //Set image (or base image, small image whatever you want
        $imageFileUri = $mediaGallery->addImage($product, $imageFile, null, false, false);
        $mediaGallery->setMediaAttribute($product, 'image', $imageFileUri);
        $product->save();
    } catch (Exception $e) {
        Mage::logException($e);
    }

place the below code in a file which is in root directory and execute the code. Please take the backup of your database before running the code.

<?php 
require_once('app/Mage.php');
umask(0);
Mage::app();

$collection = Mage::getModel('catalog/product')->getCollection()
        ->addAttributeToSelect(array('image', 'thumbnail', 'small_image'))
        ->addAttributeToFilter('thumbnail',array('neq'=>'no_selection'));

foreach($collection as $product){
    $path = "Path_of_image_here";
    if(is_file($path)){
        try {
            $product->setSmallImage($path)
            //->setThumbnail($path)
            //->setImage($path)
            ->save();
        } catch (Exception $e) {
            echo $e->getMessage();
        }
    }
}