Painting en plein air is like bowling...there are hundreds of things to think about (all at the same time). In bowling, the object is to knock down all the pins. In painting, the object is to ---- well, there's the kick. Does the artist render the painting as an identical twin of the object being painted? The artist may chose to do that, but there are hundreds, thousands, millions of other possibilities. Changing the background, the foreground, the colors, the shapes, adding or omitting items, moving things around a bit (or a lot) - there's just so much to consider when doing a painting.
There are also choices of subject. Do I paint the whole world? Or just one little corner? Or just one flower? Where do I set up my easel? Where do I stand? Or do I sit? Or perhaps crouch to get that perfect perspective?
Did I remember to consider the sun's movement across the sky when I chose the subject and easel placement? How will the subject remain lit as I paint? Or will the tree shadow encroach too soon? Will my canvas/palette be well lit but still in shadow during the painting process? And if not, where did I put my painting umbrella? (There is broken sun/shade falling across the canvas in this photo...which made painting more difficult.)
Choices --- every artist makes hundreds during the creation of a single painting. A photograph captures just what the lens sees - no more, no less. A painting is filtered through the eyes and mind of the artist, which makes each original painting a unique piece of artwork.
And original art makes a unique gift. Christmas is coming (again) this year.