No one can visually identify mold. Black substances like these must be tested to determine if they or are not mold. When a suspicious substance like this is found logic dictates a swab sample be taken and analyzed. In addition to having surface samples taken mold air testing is also highly recommended in order to determine how much and what type mold may exist within the air that one is breathing in.
There happens to be one black mold that is a very bad pathogenic mold. There are other black molds that are not anywhere as harmful. Mold comes in every single color of the rainbow. It is estimated there are tens or maybe even hundreds of thousands.
Prior to taking any action to remove or remediated mold one must first find and cure the source of moisture. If one were to spend thousands or even tens of thousands of dollars on mold remediation and not cure the moisture problem one can expect the mold to start growing again and for additional funds to be expended once again.
There are three things needed for mold to grow. Mold spores in the air (nearly always the case), something for the mold to eat (like the wood and drywall paper your house is made of) and moisture. Notice the only one under the control of the home owner is moisture.