The most straight-forward solution would be to include the Product Image in the emailed gift card.
To do this, override the email template by copying this file:
/wp-content/plugins/pw-woocommerce-gift-cards/templates/woocommerce/emails/customer-pw-gift-card.php
To here (you may need to create the subfolders if they do not exist in your theme folder):
/wp-content/themes/<your-active-theme>/woocommerce/emails/customer-pw-gift-card.php
Once the file is in your theme folder, open it up in a text editor and make any changes. You can change colors, wording, etc.
To set the background image to the gift card product image, find the code below and uncomment the three lines as shown:
.pwgc-gift-card-container {
border-style: solid;
border-width: 1px;
border-color: #333;
border-radius: 16px;
background-color: #FFFEE0;
padding: 0px 24px;
<?php
// If you want to show the gift card product image you can do something like this (uncomment the next few lines by removing the two slashes):
$image = wp_get_attachment_image_src( get_post_thumbnail_id( $item_data->parent_product->get_id() ), 'single-post-thumbnail' );
echo "background-image: url('$image[0]');";
echo "background-position: center;";
?>
}