Blank check is a minor /b/ meme that was first posted 2006/03/05, featuring a character who was drawn on 2005/05/14 by manga-ka Higuri You, but with the face erased. It came with the message "I've given you a blank check, go crazy". Within an hour, over 100 different faces were given to the image posted, using memes such as Koffing, Cockmongler, V and Tom.
The image was most likely given the name Doppelgänger from the Sandwhich guy post with the text, "Nice try Doppelganger! Save it for Queen Doppelpoppolus!"
Doppelgänger is literally a window to the past, in that you can look at the memes of old through it.