Total Depravity & the Image of God

What is meant by the expression Total Depravity? I think the expression conjures up many different ideas. Some think of a depraved creature as an evil freak of nature. It would be something from which everyone would run in horror. For others, a depraved human is someone who looks deceptively good on the outside, but who is always plotting evil deeds on the inside. Even what may appear to be a noble deed must have some evil ulterior motive.