Years ago, I lived with a scooterist friend who has a large poster made of a very famous black & white photo of a man racing a Vespa around a track. It looked like a huge photocopy, with the grainy pixels noticeable. While I don't recall he exact dimensions, it was two long sheets of paper that when put together were something like 3 x 5 ft. It was impressive and gave us a cool scooter house advantage.
Now, with technology making custom printing more accessible, the dream of having a cool, but well-done custom wall treatment is simple. Check out Wall Collection, a Danish company that can create custom wallpaper for you using your own artwork.
Checkout some examples of what they have done:
While prices aren't listed on their site, they do charge $60 for shipping to the US. May be a cool ay to turn your basement or spare bedroom into a scooter shrine.