Answer:
Yes, by several methods - audio recording, video recording, Infrared video recording are the most common methods. Other methods such as EMI meters are theoretical based on experience and observation, as are barometric readings, humidity, temperature, etc. Audio and Video are generally the ones most people look to for evidence though.
As far as seeing or hearing a ghost, it's always when you least expect it, or at a fleeting glance. The most common form is a shadow entity (shadow people, etc.) and appears as a black, shapeless form roughly in the outline of a human. Sometimes they are there but you cannot see or hear them, but they will affect you anyway (eyes tearing up, cold spots, goosebumps for no reason, etc.).
It is hard to explain unless you've actually experienced it. Some in our group have been poked and prodded by ghosts and you cannot see them. Ghosts need a lot of energy to manifest (or so the theory goes, and it's not a bad one), and many lack the ability to fully manifest enough to be seen.
TSD -RAVEN-
Category Supervisor