Optical Illusions

Image: Flickr

All the lines are straight. Image: Wikimedia Commons

Image: Aaron Fulerson on Flickr

Concentric circles. Image: Justin Hanes on Flickr

All the lines are straight and parallel. Image: Wikimedia Commons

Image: Printerval

Image: Just Color

Image: DeviantArt

Image: Openclipart

Image: Picryl

These are circles, not spirals. Image: Justin Hanes on Flickr

The horizontal lines are straight and parallel. Image: Wikimedia Commons

Image: Justin Hanes on Flickr

Image: Justin Hanes on Flickr

Image: Justin Hanes on Flickr

Image: rawpixel