As exemplified in OPs images, a majority of pinup art was drawn or painted. The model posing was often enhanced by the artist. Longer legs, perfect skin, breasts that defy gravity and just the right light. In the 50s photos became popular. And remember that photoshop just does digitally what a good darkroom master did.
All pinup art celebrates the beauty we see in women. Women that remind us of that art can intensify the fantasy we are acting out.