Okay, the last person to be identified in the picture (seated right) is Jean Taubenhaus, a chess player from Warsaw, Poland.

 He ended up finishing in 8th place at the 1893 New York tournament.

 Thanks for all of the participation.

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The player in the bigger portrait on the wall is obviously Wilhelm Steinitz.  The player in the smaller portrait, referred here as "Generic 19th Century Bearded Man, taking a break from posing for cough drop boxes" is actually George Henry Mackenzie.

 Mackenzie was a former U.S. Champion, whose major claim to fame was winning the 2nd, 3rd, and 5th American Chess Congresses.

The location is the Manhattan Chess Club (as stated by Claypot) in 1893.

Hint: The gentleman across from Pillsbury played in the 1893 New York tournament and is seen in the group picture from that event.

Jackson Showalter?

edit: i see claypot beat me to that guess. 

I agree with Jasn... "Generic 19th Century Bearded Man, taking a break from posing for cough drop boxes"... hilarious...

Could the player to the right be Jackson Showalter doing his impression of Steinitz?

I know that's a portrait of Steinitz glowering down on them!

Pilsbury's opponent is Generic 19th Century Bearded Man, taking a break from posing for cough drop boxes.

Check out the cool chess clock. 

Harry Nelson Pillsbury is correct (seated on the left).  The man on the right is not Zukertort or Tarrasch.

Hint: This was from a tournament in 1893.

Marshall (l) - Tarrasch (r) ?

Zug