See that little SpongeBob Squarepants in the fresco? No? Look again, bottom right. To give you an idea of just how close you can zoom into this image from
Halta Definizione , here he is again in all his glory...
Digital photography is taken to extraordinary levels of detail on this Italian site, with paintings from Da Vinci, Bronzino and Botticelli among others.
Here are a couple more details from one of my favorites, Andrea Pozzo's illusionistic masterpiece of perspective in fresco painting; the ceiling of the church at San Ignazio.