Hi，can the visitor check the luggage in gallery?

Yes

Yes. Check room is immediately past the Constitution Ave entrance.

I checked in a travel sized backpack (35 liter) and the cubbie they put it in was large.

There is a check room, bag goes through a security scan and you get a bag # that you use to collect your bag later.

I saw a check room but bring bags gets you pulled aside to view what is in it most likely.

There is a check room. You can look at the policies on the website. Good luck.

Not sure about full size luggage .They do enforce if you have a backpack, even a purse style one that it can only be on one shoulder.