The picture is awfully small.
The car may have been temporarily lettered with whitewash, previous to its final lettering (with data).
The shadow of the latch bar, and other "flaws" could have been touched up on the negative (in black ink) or on a print.
It also looks like the print may have been dodged around the lettering. May.
I also see some streaking downwards from the letters. I doubt that feature would have been added if the lettering was done on film or paper.
The background "color" on the car looks a bit mottled. Interesting.
It'd sure be nice to see that picture bigger!