Images are merely light as it impinges on our eyes. Shadows are light failing to reach some surface because of something that stands in the way.

There is an interesting asymmetry between the two - 'asymmetry' is not symmetrical, though nearly so. Being a word that describes itself, it is autological (if it did not describe itself, like 'monosyllabic', for example, it would be heterological). 'Asymmetry' has a suggestion of symmetry about it, it is almost in a grey world between heterological and autological, defying the pigeon hole principle, but not quite.

Of course, there is the age old question, is 'heterological' heterological? Hyper-dimensional pigeons fly out the window, the world is unhinged.