Interactive optical illusion

Text next to these drawings is 'Interactive optical illusion' and 'look through camera lens at object'. First of all it isn't interactive unless I am expected to tell it something, and secondly because of all this Blipping malarky, I don't look at anything unless it is through a camera lens.

Anyway, I think the grey liney thing is supposed to miraculously appear 3D instead of just badly drawn. What is well drawn is this motley bunch of tourists and slightly tipsy locals (me), all staring, squinting and snapping away. Listen, it might be a great optical illusion, because i don't know how many hours I spent staring at those white noise pictures waiting for a 3D dolphin to appear. I mean i spent hours staring at those fucking things while some smug git is telling you to 'look through it' or 'you're concentrating too hard' or whatever. Autosterograms i think they were called. Not much call for them now though.