Sandman's comments to use a couple or three features to identify a fish is sound; I recall that very same advice on a similar thread a year or two ago.
Caudal fins can be deceiving. Pink and chinook tails are heavily spotted and at first glance can be confused. A coho with just a few faint spots on the upper lobe of the caudal can be confused for other species, as can a coho with spots on both lobes.
I caught a jack spring a few weeks ago off the beach. I was expecting a coho, and spots on the upper lobe of the caudal confirmed my initial assumption. Then I caught a whiff of the little bugger! Hold on...
A more thorough look at the entire caudal, and I think a peek at the gums too, confirmed the unexpected. Point being, you can be fooled by your expectations.