Hidden message… Blur & figure-ground reversal
Above you see –most probably– an apparently random array of blocks. Blurring the image reveals an unexpected message of doubtful soundness.
Instead of blurring, you can move the mouse pointer over the picture (select a central block), causing it to shrink with accompanying blur. On purpose, the shrinking is a bit tricky… but you can also hit the shift key.
Comment. The strong spatial low-pass filtering removes the 3-dimensional masking cues, enabling a re-evaluation of figure and ground.
Sources. I once saw this in Spillmann’s lab, the animation above is based on an image I found as “eye test”. The original source seems unknown. Please step forward so I can acknowledge!