I have never seen reference to a contemporary image of Jose Altamira. If there was one it would have been a drawing or painting. My suggestion is that your nephew draw a picture of him. He arrived at Monterey in 1820, age 33. He did not make a favorable impression.
Fr. Payeras wrote of Altimira: "His actions will reveal his merits; for this he lacks neither talent nor still less application." He was impulsive, political, hot tempered. In the definitive biographical dictionary Franciscan Missionaries in Hispanic California there is this telling paragraph "Altimira was a sort of "Young Turk" missionary, a type that would not be frustrated..."
The galleries on our website (particularly 19th century drawings and the Franciscans) will give him some images of padres to start from. The key things is how does your nephew envision him. I would love to see a copy of his picture.