In the standard model for a lens straight lines in the subject of a photograph will always end up straight. However I have seen a variety of photographs in which straight lines end up being curved, e.g. the horizon tapers down at the edges, or a fence near the photo border is mildly curved.
What could cause straight edges to come out curved in a photograph? I have no idea what cameras were used in these cases, but I am certain they are standard consumer grade cameras (so they aren't fisheye type lenses such as equisolid angle lenses). Believe it or not I have to make computations based around objects in photographs and have no way of accounting for why straight things turn out curved in some photographs. From what I know about optics, this shouldn't happen, but it does, so I am missing something. What is it?
Can anyone give authoritative information about this?