From StarWars.com
"Topps now takes the artist sketch card concept to the next level in Star Wars Galaxy 4 series with all-new sketch cards by underground artists from the hip-and-urban world of designer toys. Topps has recruited several of these artists to put their own stamp on their first-ever set of die-cut sketch cards. Blanks in the shape of Darth Vader and stormtrooper helmets have been dispatched for customizing by such artists as Sket-One, Evil Design, MAD, Gargamel, Mishka, JK5, Onell Design, Suckadelic, Kaiju Big Battel, and many more."
Check out the above link for more information.

See also:
The Return of Star Wars Galaxy Trading Cards
Topps Star Wars Galaxy IV Artist Spotlight: Grant Gould
Topps Star Wars Galaxy IV Artist Spotlight: Kevin Graham
Topps Star Wars Galaxy IV Artist Spotlight: Jessica Hickman