Here's how to display some additional data in woocommerce_before_order_itemmeta :
add_action( 'woocommerce_before_order_itemmeta', 'so_32457241)before_order_itemmeta', 10, 3 ); function so_32457241_before_order_itemmeta( $item_id, $item, $_product ){ echo '<p>bacon</p>'; }
I do not know how you save your data, so I can not make a more accurate proposal. Keep in mind that immediately after this hook everything that you saved as the metadata of the order items will be automatically displayed.
Image filtering is more complicated. I found this gist at the beginning, but it requires some custom conditional logic, since you do not want thumbnail filtering everywhere, but only in orders.
Edit: Currently, the best I can do to filter element thumbnails is:
add_filter( 'get_post_metadata', 'so_32457241_order_thumbnail', 10, 4 ); function so_32457241_order_thumbnail( $value, $post_id, $meta_key, $single ) {
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