We do need a way to set a caption here. Writing it over or under the image does not associate them.
Template talk:Graph:Population history
Would be really neat if this had labels with year and population that appeared when you hovered over a data point.
It would be (and relatively easy to do), but for that one would have to activate (play) the graph. Plus the graph would have a play button on top of it, just like in some graphs in Extension:Graph/Demo.