"Art in Detail: 100 Masterpieces" by Susie Hodge illuminates obscure details in well-known works of art.

The screaming figure in the center of "The Scream" is the obvious focal point, but what's to be made of the shadowy figures in the background? According to Munch, they're two friends who walked on without him when he stopped and stood "trembling with anxiety" during a stroll.
The neoclassical "Oath of the Horatii" depicts three Roman brothers saluting their father, who's holding their swords, before going off to fight rivals from Alba Longa. In their shadow, their mother huddles around her grandchildren.

"The older boy cannot refrain from peeping out in awe at the men and their glittering swords -- demonstrating that to lay down one's life for one's country is honorable and something for which all men should be prepared to fight, even from a young age," Hodge writes.
At first glance, this 15th-century painting seems fairly realistic -- until you take a closer look at the horses, who are in stiff, unnatural poses.

"Prior to the photographic studies of motion by Eadweard Muybridge in the 19th century, most people were unaware of how animals move," Hodge writes.
The ornate Latin script above the mirror in the background is not an ancient expression. It's merely a cheeky translation of "Jan van Eyck was here 1434."
Here, eight-year-old Jesus Christ holds a candle for his stepfather, Joseph. The auger Joseph is using to drill a piece of wood creates the shape of the cross, referencing Jesus' future crucifixion.
The man behind the canvas is none other than Velázquez himself. This is the painter's only known self-portrait.
Tilt you head and take closer look at the disc in the foreground: it's a distorted image of a skull. An example of "memento mori" -- a reminder of mortality -- it's meant to remind the viewer of heaven, hell and the afterlife, and the implications of our actions on earth.
Huddled before the future Emperor Baldwin IX, three citizens (including a small child) plead for mercy. "The crusade was primarily a French undertaking, yet (French painter) Delacroiz presents an empathetic view of the Byzantine citizens who have suffered," Hodge writes.
The golden rapier pommel subtly poking out from the crook of the sitter's arm was meant to suggest he was a skilled swordsman -- the mark of a gentleman during that era.
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It’s easy to take a well-known masterpiece at face value. However, many of the world’s most renowned works come loaded with underlying messages and back stories. Artists use specialized techniques and subtle symbolism to hint at larger themes, expand on a narrative or – in some cases – add a touch of humor.

Incredible photos show you the world as you've never seen before

“Art in Detail: 100 Masterpieces,” written by Susie Hodge, sets out to illuminate the obscure details that the average passerby is likely to miss as they flit between the galleries at the world’s most prestigious art institutions.

“Looking at any work of art is a personal experience,” Hodge writes, “but one that always benefits from a wider knowledge and awareness. The more you know and the closer you look, the more you will see and enjoy.”

Check out the gallery above for a closer look at some of history’s most groundbreaking masterpieces.

“Art in Detail: 100 Masterpieces” by Susie Hodge, published by Thames & Hudson, is out now.