There may be a new contender for the oldest extant illustrated garment. Until now I thought it was the c. 1610 jacket of Margaret Layton, but Daniel Milford-Cottam alerted me to a possible earlier garment worn by Eleanor of Toledo in one of her last portraits that was also possibly her burial gown.
Spanish aristocrat Eleanor of Toledo married into the Tuscan Medici family at the age of 16. The union brought blue blood into the Medici clan, money into Eleanor’s family, and produced 11 children. Ill health plagued Eleanor most of her life and in 1562 she died from Malaria at about age 40.
In the 19th century her tomb was opened and body exhumed. The funereal dress she had been buried in was removed and is now kept in the Pitti Palace in Florence (the home bought by Eleanor and Cosimo Medici in 1549 that became the residence of the ruling families of Tuscany.) The sleeveless dress has metallic embroidery that seems to resemble what can be seen of the same bodice in one of her last portraits.
There is an interesting article that talks more about Eleanor of Toledo’s portraits, gowns and makes the initial supposition that the burial garment may be the one shown in her portrait.