Photo Credits
The Geller Yeller, the demo paper on this site, uses photos of set replicas and studio-tour sets from Wikimedia Commons. Each one is used under the license shown, and none of them are stills from the show. In the papers they are cropped and toned to suit each style, and those versions are shared under the same license as the original.
The photos

The orange couch at Central Perk, with a coffee table in front of it. Photo by Stuart1000 (English Wikipedia), Public domain. Source

An acoustic guitar on a stand beside a leopard-print chair at Central Perk. Photo by Chester from Toronto, Canada, CC BY 2.0. Source

Monica’s purple apartment, with the kitchen table and the balcony window. Photo by O2Q357Ys, CC BY 4.0. Source

An orange couch and armchairs under a neon sign. Photo by Nielsoncaetanosalmeron, CC BY 4.0. Source

The Central Perk front window, with the coffee-cup sign in it. Photo by Benoît Prieur, CC0. Source

Central Perk from the counter, with the couch and the mismatched chairs. Photo by Stuart Sevastos, CC BY 2.0. Source

The inside of Central Perk, with the couch in front of the counter. Photo by Gga2015, CC BY-SA 4.0. Source