Objects moving across the light signal, I don’t think, would effect it very much, unless they were sufficiently massive to gravitationally distort the image. However, there are examples where the light from far distant quasars is “intercepted” by enormous clouds of hydrogen gas between us and the quasars. The light still manages to get through, but various spectral lines are absorbed by the gas. Many batches of absorption lines, each representing a different cloud of gas at a different distance from Earth, can be seen in the spectral signature of the quasar light.
See “Lyman-alpha forest”
http://en.wikipedia.org/wiki/Lyman-alpha_forest