Picture Of Coffee Cups

In the Central Perk, Whose picture is it?

Hi, guys.
I’m a huge fan of the TV show “FRIENDS”
Anyway, I really like the pictures on the wall in the central perk cafe.
Sometime it was a big Coffee cup, sometimes it was Uncle Sam and there’s more. I really like the style of the pictures.
I’m sure it’s from same artist but I can’t find who he/she is.
Does anyone know whose picture is?
Thanks

The artwork in Central Perk is changed every 3 episodes. The art department showcases local, national and international artists. Some artists create original pieces just for the show!

edit: this site has 4 tshirts with different paintings from the central perk on them: http://home.planet.nl/~hmansens/clothing.htm

edit: this website says this lady, jules burt is responsible for the paintings.

http://www.jou.ufl.edu/pubs/onb/F05/portrait.html