If you can see mold growth and/or smell a musty odor, you have a mold problem.  However, it is recommended that you do a thorough inspection to determine the source of the mold growth.

Mold growth resulting from a leaky shower stall

Mold growth from elevated crawlspace moisture.

Mold growth in an attic resulting from a leaky roof.

Mold growth inside the framed wall resulting from a flooded basement.