See the Creative Cow tutorial on a free After Effects / Photoshop plug in replicating the Droste effect.
Prompted by the availability of the first microscopes in the 17th century, a theory arose that either the egg or sperm, until then unseen, contained a miniature human. This human, (or animal or plant as the case may be) would then simply grow to full size. A priest philosopher, Malebranche, expanded on this idea. He added that inside the first human lay yet another preformed human, and within that another. This went on ad-infinitum, like endless Russian Dolls. He concluded that all humans were therefore preformed in the bodies of Adam and Eve in the garden of Eden. This theory thrived as it suited the Church.
The lens maker, Nicolaas Hartsoeker, who at one time made instruments for the Paris Observatory of astronomy, claimed to have seen the small human within or at least he made a sketch of what he believed to be there.
The first lenses were found in Assyria, in the Mesopotamia, dating around 700 BC.