How would I know if something that looks like it might be mold IS mold?

[Grasswire2]

I pointed out a couple of "interesting" spots to my landlord during annual inspection a couple of weeks ago. He said they weren't wet, so they couldn't be mold.

But one of them is in the ceiling of a closet that has an old water stain. It's a black spot.

The other is outside our door that separates the bedroom from the common laundry room in the basement, and water DOES come in the laundry room when a hard rain or when the landlady leaves the sprinkler on; many times in a year. The puffy pocked area is at the bottom of a wall that is drywall, I guess. That one is kind of puffy and bigger. They aren't concerned about the water coming in and pooling there, although the washer, dryer and freezer sit in the area that's wet at times.

I realize that under state law there are implications if I send him a proper notification-of-mold letter. But how do *I* know, really.

Any thoughts?