Marques Lutèce, St & Co.à D and H.O. Actually St & Co.à D is just an early French branding of Stengel & Co, Dresden, for which Ostheim was presumably the French or Paris agent. I haven't found a card bearing the H.O. logo. Ostheim used "Lutèce" on views of Paris (see first example), Lutèce was the name of Paris in early times. The example card dates from around 1899 when the text République Francaise (used from 1896) was replaced by Carte Postale. Incidentally the reason these lines are often crossed out, as in the other example, was because if the card had no written message it could be posted more cheaply as printed matter.
A card in Carte Lutèce series 1, a coloured card, was printed by Vaugirard.
The following information was sent to me by Gregoire Clemencin: Re. HO / Henri Ostheim, I identified this gentleman as the photographer referred to by many as Henri Oltramare. My view is that Henri Oltramare is a name made up by someone to match the HO initials. Indeed, he started his Parisian career as a representative for German book publishers, then for postcards and finally started his own business as a photographer of nudes, many of which being reproduced in so-called art magazines but also as postcards but then unattributed.