Serendipity exists for a reason, I always say. When I published my post There is no W in Paris a few days ago, I was unaware of the Alphabet photo challenge. But since I have a photographic alphabet, why not enter the challenge?
The astute reader will notice that the alphabet grid is 5 by 5, containing 25 letters. A clue to the missing letter is contained in the name of the referenced post. And I am beginning to wonder about K.
Hint: turn the M upside down.