According to an "old wives' tale", a ghost's self-image determines how it projects its "ectoplasm" to form the image that living people perceive. In other words, if a ghost's self-image is that of a sexy, seductive vampiress, then that is how it will appear -- clothes, hair, fangs, and all -- and it's the viewer's own fear that attracts and gives power to such evil things.
But ghosts do not exist, so no worries.
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The mere fact that science may not yet adequately explain an object, event, or experience does not mean the immediate explanation should automatically default to a conspiratorial, extraterrestrial, paranormal, or supernatural cause.