As all know every big system has a way to index the catalog on flat tables , not logic to make query for example directly on oro_proudct because they has many complex relation with other tables , So to get fast frontend display with best performance using a simple tables as source of data . 
OroCommerce  System has a website indexer tasks which you can done with oro command :
bin/console oro:website-search:reindex

Your catalog data will pushed in some flat tables is:
oro_website
oro_website_search_datetime
oro_website_search_decimal
oro_website_search_integer
oro_website_search_item
oro_website_search_text

For example oro_website_search_text stock data of type text or string …

Let’s start explore how the image get showed in frontend product list page firstly we shuld know who’s the datagird responsible , go to vendor/oro/commerce/src/Oro/Bundle/ProductBundle/Resources/config/oro/datagrids.yml , So search for frontend-product-search-grid :

 
    frontend-product-search-grid:
        options:
            entityHint: oro.product.entity_plural_label
            displayOptions:
                selector: '.catalog__filter-controls__item_display-options'
            jsmodules:
                - oroproduct/js/app/datagrid/frontend-product-display-options-builder
                - oroproduct/js/app/datagrid/frontend-product-filters-events-dispatcher-builder
            frontend: true
        source:
            type: search
            search_index: website
            query:
                select:
                    - text.sku as sku
                    - integer.newArrival as newArrival
                    - text.names_LOCALIZATION_ID as name
                    - text.shortDescriptions_LOCALIZATION_ID as shortDescription
                    - text.type as type
                    - text.image_product_medium as image_product_medium
                    - text.image_product_large as image_product_large
                    - text.product_units as product_units
                    - text.primary_unit as unit
                from:
                    - oro_product_WEBSITE_ID
 

You can see that the query select the collection from flat tables but the more important fields :

 
                    - text.image_product_medium as image_product_medium
                    - text.image_product_large as image_product_large
 

and see the function  onResultAfter :

 
    public function onResultAfter(SearchResultAfter $event)
    {
        /** @var ResultRecord[] $records */
        $records = $event->getRecords();
        $this->addProductUnits($records);
        $this->addProductImages($event, $records);
    }
 

You should know datagrid offering many event pre Build ,after build  and after result ….

 
  - { name: kernel.event_listener, event: oro_datagrid.search_datasource.result.after.frontend-product-search-grid, method: onResultAfter }
 

result.after : after building the datagrid and get collection from db you have the ability to make some change like change some data of datagrid records.

So let’s explore the function addProductImages($event, $records) :

 
    protected function addProductImages(SearchResultAfter $event, array $records)
    {
        $gridName = $event->getDatagrid()->getName();
        $theme = $this->themeHelper->getTheme($gridName);
        switch ($theme) {
            case DataGridThemeHelper::VIEW_LIST:
                $imageFilter = self::PRODUCT_IMAGE_FILTER_MEDIUM;
                break;
            case DataGridThemeHelper::VIEW_GRID:
                $imageFilter = self::PRODUCT_IMAGE_FILTER_LARGE;
                break;
            case DataGridThemeHelper::VIEW_TILES:
                $imageFilter = self::PRODUCT_IMAGE_FILTER_MEDIUM;
                break;
            default:
                return;
        }
        $noImagePath = $this->imagePlaceholderProvider->getPath($imageFilter);
        foreach ($records as $record) {
            $productImageUrl = $record->getValue('image_' . $imageFilter) ?: $noImagePath;
            $record->addData(['image' => $productImageUrl]);
        }
    }
 

So related the row view if grid or list add data to records large or medium:

 
        foreach ($records as $record) {
            $productImageUrl = $record->getValue('image_' . $imageFilter) ?: $noImagePath;
            $record->addData(['image' => $productImageUrl]);
        }
 

Watch video for more infos.