Knocking bird

This bird has been knocking on my window (in Maryland) daily for the past 2.5 weeks. It looks like some type of pigeon as well as a blue jay without the peak. It is bluish-grey on top and tan and white underneath. Since I do not know anything about birds; therefore, I would like for someone to tell me what type of bird this is.

Any information regarding this bird would be helpful.
By the way, the picture is real, the bird is holding onto the window screen.