I've moved into a new apartment for a while. Is this mold? Is it safe to continue live here?
Looks more like mildew, which is related to mold, but not as dangerous (from a health standpoint). Yes, a dehumidifier could help prevent mildew. I would also look for sources of the moisture, e.g. a clothes dryer that is not venting to the outside, a bathroom vent that is not functioning (or non-existent), water leaking somewhere etc.