Is it possible to count cards by literally counting cards?
The answer is almost certainly no. Card counting is used primarily to determine how much to bet - a standard strategy might look like:


-1 or smaller: find a better table
-1 to +1: bet table minimum (still in casino's favor but worth waiting around)
+1 or higher: start betting big (the game has tilted in your favor)


Now I haven't run the simulations, but my guess is that the correlations you'd find are too small, e.g. Two cards = -0.05; Three cards = 0, Four cards = +0.05. Unless any of the numbers are greater than 1 or less than -1, you can't do anything useful with the information.

Ultimately, I think if it were as easy as counting the cards on the table, everyone would be doing it.