<?php

// vendor/ModuleName/Setup/InstallData.php or
// app/code/vendor/ModuleName/Setup/InstallData.php

use MagentoCatalogModelProduct;
use MagentoEavModelEntityAttributeScopedAttributeInterface;
use MagentoEavSetupEavSetupFactory;
use MagentoFrameworkSetupInstallDataInterface;
use MagentoFrameworkSetupModuleContextInterface;
use MagentoFrameworkSetupModuleDataSetupInterface;

class InstallData implements InstallDataInterface
{

/**
 * @var EavSetupFactory
 */
private $eavSetupFactory;

/**
 * InstallData constructor.
 */
public function __construct(
    EavSetupFactory $eavSetupFactory
)
{
    $this->eavSetupFactory = $eavSetupFactory;
}

/**
 * Installs data for a module
 *
 * @param ModuleDataSetupInterface $setup
 * @param ModuleContextInterface   $context
 *
 * @return void
 */
public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
{
    $setup->startSetup();

    /** @var MagentoEavSetupEavSetup $eavSetup */
    $eavSetup = $this->eavSetupFactory->create(['setup' => $setup]);

    $eavSetup->addAttribute(
        Product::ENTITY,
        'mouseover_image',
        [
            'type'                    => 'varchar',
            'label'                   => 'Mouseover',
            'input'                   => 'media_image',
            'frontend'                => 'MagentoCatalogModelProductAttributeFrontendImage',
            'required'                => false,
            'global'                  => ScopedAttributeInterface::SCOPE_STORE,
            'used_in_product_listing' => true,
        ]);
      $setup->endSetup();
    }
}