At (broadcast, with ads) 22 min., they hold up a very dark film negative and say it is "underexposed." An underexposed negative is light or clear.
When Perry is talking with Bill Cotton after putting out the fire in Cotton's shop, the room is still full of smoke yet neither of them reacts to the smoke in the room by coughing or covering his mouth and nose to keep from breathing it. The "smoke" is obviously fake.
The note says either Brandon refuses the appointment, or "the newspapers gets these pictures . . ." Mason, however, reads the line correctly: "the newspapers get these pictures . . ."
After the "fire" in the camera shop, it appears the walls/fixtures have simply been "fogged" by black aerosol spray paint to give the appearance of fire/smoke damage.
The typed blackmail note that also came with the photos given to Perry has two grammatical errors in it. First, part of it reads "newspapers gets." And, since the note reads "newspapers" (plural), then the last word in the note should read "editions" (matching the previous plural). BTW, when Perry reads the note out loud, he does not repeat the first error ("newspapers gets"), but he does repeat the singular form of "edition."
When Perry drops by Bill Cotton's camera shop to question him, it is approximately two in the morning, much later than the time such a business would close.