I think this depends on the situation. If one faces a lot out of an obsolete household with lots of albums, transparency boxes etc. one could deduce that people thought about what they give away and thus lost interest. If it's just a film inside a camera one could deduce that it might have been overlooked.
Originally Posted by Vaughn
But even in the former case, the lot may come from a suddenly deceased person which did not wanted those images to be spread.
Furthermore in parts of the world there is legislation on publicizing photographs of persons. So even in case one has acquired legally old prints, films, transparencies, you might still not be allowed to do everything you like with those.