Since the Renaissance, artists have enjoyed making optical illusions and putting minute, hidden details in their artwork. Sometimes these are easy to spot, other times, like in Hans Holbein the Younger's Two Ambassadors you need to look a little closer…

Looking at the painting, it's easy to be distracted by the rich objects and clothes on display, you might not have noticed this strange mark on floor between the ambassadors feet. But if you look at your screen from the top-right corner, you might be in for a fright!

The astronomical instruments are painted accurately, it's just a shame that many of them are incomplete. It's been suggested that this is because Holbein was using disassembled and partially broken ones from the workshop of Nicholas Kratzer as props.

There are many reasons for hiding details in artworks - flattering people, making jokes, or simply showing off your own skills as an artist. And if you were in any doubt that  Rembrandt van Rijn painted The Anatomy Lesson of Dr Nicolaes Tulp, then just take a closer look…

The writing's on the wall! At the top of the picture is a little signature that appears to have been written on the wall behind the class, reading Rembrandt, 1632.

… and if you tilt your head to the left, you'll see the navel of the corpse is painted as a capital R.

Joris Hoefnagel was an illustrator of manuscripts known for his almost-lifelike renderings of plants and animals. Here, he decorates the a page of Georg Bocskay's calligraphy manual Mira calligraphiae monumenta with a flower that seems to pierce the page.

Turning over the parchment, the lettering and illustration of the previous page are just about visible. To this, Hoefnagel has added another detail of the stem. Bocskay's calligraphy may be beautiful, but art will always be more entertaining!

Gerard Houckgeest adds wit and levity to this scene of a whitewashed church interior by including a painted curtain and rail.

At the time, paintings were often hung behind curtain rails for protection from damage by light and dust. This little addition shows how Houckgeest can master both the grand architecture of the nave, and the intimate space of the owner's home.

A pile of papers, pamphlets and musical scores litter Cornelis Norbertus Gijsbrechts' illusionistic painting of a letter rack. You can imagine doing a double take when you saw this hanging inside a private study.

Every single scrap of paper is incredibly detailed, covered with writing and miniature wax stamps that add to the realism of the painting. In fact, you might recognise that name on the etching…

… and in the top left corner behind a sheet of paper is a little comb - a small hint that you should go through this painting with a fine-toothed comb if you want to appreciate every detail!