According to Gwara, he hatched this idea about a year ago. He worried that after the release of the Zemeckis Beowulf film, it would be difficult to imagine the monsters in Beowulf without envisioning those images -- much as many people now see Bilbo Baggins as looking like this, not like this. Gwara wanted to capture time before the film, when the imagination of the individual artist was more important than a shared cultural image.
Gwara began collecting images from Beowulf, particularly images of Beowulf, Grendel, and Grendel's Mother. He currently has about 40 items on display at the library, his favorite of which are the Henry C. Pitz illustrations. Pitz's illustrations were included in the 1033 Stafford Riggs book The Story of Beowulf. The exhibit describes it:
Pitz’s stylized Art Deco illustrations of Beowulf are among the most famous ever produced. In this scene Beowulf kills a much smaller dragon than the fifty-foot specimen in the poem, but the scene is full of dramatic energy: the dragon’s wings folded within the frame and its leaping posture, the hero’s open stance, the thrust of the sword, and the suggestion of flame radiating from the dragon’s mouth.
His absolute favorites are ones that he couldn't get for the exhibit, mostly because they are either unavailable or too expensive. One is a palm-sized children's book called Brave Beowulf, that recently sold for about $180 on e-Bay. The others are in a book called Early Myths of the British Race by Rosemary Sutcliff (though he does have illustrations from other Sutcliff books in exhibit). If any Wordhoarders happen to have these images and would send them to me, I'd be happy to post them.
Gwara's own preference is for images that are more like illustrations, and less like artwork. After about the 1950s or '60s artists began to favor line drawings and woodcuts, which he considers the low point of Beowulf illustration. His own favorite illustrators are from the comic books, especially from DC Comics and Gareth Hinds.
Though it isn't Gwara's page, you can find an online collection of Beowulf art here.