[HiTech RedNeck]

What’s the rectangular confetti like stuff in the picture (for example, falling off the top of one of the background buildings).

[Cyber Liberty]

It looks like a building in the background is in the process of collapsing, and those are falling bricks.

[Martin Tell]

Those are bricks, falling off a leaning building. All the buildings, with the exception of the pawnbroker's, are poorly built, in disrepair, and generally falling down. If you look closely, there is a suicide (hanging) in the building on the right. Everywhere is death and insanity - just the thing to pick you up on a sunny afternoon!

Google "Hogarth Beer Street" for the contrast. All is in order and happy; the only building in disrepair is the pawnbroker's. There's also some funny anti-French references (I suppose it's funny if you are an English history nerd and know Hogarth's symbolism).

National Lampoon once did a parody called "Coke Lane" and "Pot Street." You can probably guess what it looked like.

[Trailerpark Badass]

What’s the rectangular confetti like stuff in the picture (for example, falling off the top of one of the background buildings).

I think it's a house collapsing.