Either way, you can get your fill at this site. The Sperling Foundation offers sites that even only tangentially approach Mad Cow Disease. There's no bias on the page - well, more accurately, every bias imaginable appears to be represented. Go grab a plateful. IT Enter the world of optical illusions with this site featuring over 30 images to dazzle your eyes and fry your brain.
Most images come with a short explanation of their origin and how the effect is produced.
For those illusions that would require you to flip an image 180 degrees in the real world, a simple click does the trick here. If your curiosity is struck, check out the bibliography of over 100 paper entries. The visual perception pointer page provides links to several related sites. A singular spot in British Columbia is the source for these pages, devoted to saving rare breeds of farm animals. Not only wild creatures need protection.