That's James T. Kirk (William Shatner), Jean-Luc Picard (Patrick Stewart), Benjamin Sisko (Avery Brooks), Kathryn Janeway (Kate Mulgrew) and Jonathan Archer (Scott Bakula), in case your Trek history is foggy.
Check out the background of each captain's stamp to see one of their greatest villains looming over their shoulders. That'd be Khan, Locutus of Borg, Dukat, the Borg Queen and Dolim. And yes, that means Picard's greatest enemy is himself.
Canada Post also issued a stamp of the Borg cube and one of the shuttle Galileo. This is the second year that the postal service has offered Trek-themed stamps. Last year's batch was to celebrate the show's 50th anniversary.
The US Postal Service also issued Trek-themed stamps back in August