The best optical illusions of 2017

From this disconcerting photo of a dog to the second coming of The Dress, 2017 was a great year for optical illusions.

Below, we rounded up the most baffling images and mind-boggling designs that went viral and stumped the internet over the past 12 months.

One quick note: We've included explanations for all of these illusions, so scroll down slowly if you want to figure them out on your own.

This photo of wavy and zigzag lines is confusing the entire internet.

This image, which recently went viral, shows a mind-boggling illusion created by Japanese psychologist and researcher Kohske Takahashi. The image shows 12 pairs of lines, made up of light gray and dark gray segments, on top of a white, gray, and black background. Some of these lines appear to be wavy while others appear to make sharp, zigzag turns.

Despite what you see, all the lines are actually curvy.

Takahashi, who wrote about the illusion in the journal "i-Perception" in November, calls this phenomenon "curvature blindness." As he explains in his paper, the lines we perceive as zigzags are the ones that change color (from light gray to dark gray or vice versa) at the high and low points of the curve. Against the white and black backgrounds, these lines appear wavy. But against the gray background, they appear as zigzags. In contrast, the lines that stay consistent in color at the high and low points of the curve remain "wavy" in our eyes across the entire photo.

While he plans to research this effect further, Takahashi proposes that our brains are more likely to perceive something as a corner, rather than a curve, when there's ambiguity over which one it is. Or, in his words, our perception of corners "might be dominant in the visual system."

There are 16 circles in this image — can you figure out where?

This photo went viral in August after Reddit user i124nk8 posted it on the subreddit r/interestingasf---. When you first look at it, you probably only see a bunch of black and white lines and beveled rectangles. But if you look closely, and take your time, you'll see that there are actually 16 circles in the image. 

Scroll down and keep reading if you still can't find the circles.