I think everyone should be capable of seeing it, it just might take a bit of effort to see it. My brother gave it two not very serious tries but he failed, but my mom saw it very quickly.
You know those moments that you're just staring at something, unaware of what it is and what's happening around you, just drifting away on your thoughts (and when you land back on earth you find out you've been staring at someones boobs or something

) ? That's the look you want, totally unfocussed.
Put the spectacles close to your eyes, try to get that look (not easy when you can't see beyond the pictures). The pictures start to get blurry, and slowly start melting together. Then suddenly, they come together as one 3D picture, that seems to be a lot bigger than it actually is. It's amazing, you almost feel like you're part of the artwork.
