On Entering the Arena....

Some quotes from the series:

"Very good," said Voldemert softly, and as he raised his wand the pressure bearing down on Harry lifted too. "And now you will face me, like a man... straightbacked and proud, the way your father died... "And now --we duel." (GOF PB US Edition p. 660 Chapter 34 Priori Incantatem)

"That one of us is going to end up killing the other," said Harry.

"Yes."

But he understood at last what Dumbledore had been trying to tell him. It was, he thought, the difference between being dragged into the arena to face a battle to the death and walking into the arena with your head held high. Some people, perhaps would say that there was little to choose between the two ways, but Dumbledore knew -- and so do I, thought Harry, with a rush of fierce pride, and so did my parents -- that there was all the difference in the world. (HBP HB US Edition p. 512 Chapter 23 Horcruxes)

Entering an arena with your head held high, that's what Harry seems to be doing on this cover. Il Colosseo is still a good candidate for the arena-like scene depicted here.