WTF HAX

The lion. Regardless of its size, it would still eat the giraffe's legs, and eventually get cut it down to size.

Q: What are a giraffe's predators?
A: Only Humans

There's no way a lion would win. In the actual wild an 18 foot giraffe is faster and would easily trample a lion. In this picture ( assuming a lion could somehow get as tall as a giraffe ) it would just use its horns. Have you seen a giraffe fight? Those things aren't for decoration. One swing would crush the lion wherever it hit.

Lions tend to hunt by hiding out until the last moment and then striking, if the lion gets the first strike, the giraffe is fucked, if the giraffe gets the first hit he might knock out the lion. In this picture he's not using the tactic that would allow him to win.

Parallel: Huge strength tank versus a stealth hero who's not using stealth and has a heart.

Answer: Situation dependent.

The other issuse with this image is that its a male lion doing the hunting, when in reality female lions do the hunting and males just eat the kill.

If the lion is sentient enough to be able to utilize stilts, then I'm sorry, but the giraffe has NO chance.