The first pic is this lovely Barry Windsor-Smith illo of Conan the Barbarian from Marvel's 1975 calendar.
Next we have DC's 1976 calendar featuring Green Lantern and Green Arrow by the award-winning team of Neal Adams and Dick Giordano.
Marvel got into the Bicentennial business with their 1976 calendar showing Thor giving Ben Franklin a helping hand featuring superb art by the immortal John Buscema and Frank Giacoia.
The year 1978 finds the team of Batgirl and Robin duking it out with Plant Master and Poison Ivy with artwork by JLA artist extraordinaire Dick Dillin and Frank McLaughlin.