Splinter of the Mind's Eye was the first novel written in the (now defunct and rebooted) EXPANDED Star Wars Universe. It kicked of a publishing powerhouse of dozens of books that all tied in to the stories told by the holy trilogy... but what made Splinter unique was that it came out BEFORE Empire Strikes Back... which means Luke & Leia were still trying to get it on, no one knew Darth Vader was Luke's daddy, and Luke was far from the seasoned rebel vet we would see in Empire & Jedi.
The shirt is meant to honor the original novel by Alan Dean Foster that started the kickstarted the whole EU of Star Wars. They don't make cover art like this anymore!!!!