Galifianakis, 42, is set to wed his longtime girlfriend Quinn Lundberg on August 11.
"While it has the formal and standard details of who, what, when, where -- including Zach’s full name Zachary Knight Galifianakis and his fiancée’s, Mary Quinn Lundberg -- it is also very funny," the source said.
"Zach included a drawing of himself and his bride-to-be. He made sure he looked like a little troll, while Quinn is a stunning tall blonde princess."
Quinn, 29, is the co-founder of a charity group called Growing Voices and the one-time ballerina has done extensive volunteer work for UNICEF in Afghanistan, Bosnia, and Africa.