Perhaps. this is my favourite Maximum card is:

It shows the painting "Cičncia I Caritat" (Science and Charity) an early (1897) work by Pablo Picasso (1881-1973) who spent his youth in Barcelona, my home-town.
The work, hangs on that city's Picasso Museum.
The stamp, issued on October 1978, is on a commercial postcard, cancelled with an special postmark, used on a temporary PO, set on Barcelona's Picasso Museum, on the day of issue.
The doctor, is a portrait of Picasso's father.
I recall, seeing this painting on my first visit to the museum, with my parents & brothers, a short time after the Museum was opened on the 60s.
It was an important event in our city.