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This picture has been floating around the internet recently:

enter image description here

Is it a genuine picture or photo-shopped? Or perhaps its some sort of optical illusion similar to the wagon wheel effect?

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It's an effect of the camera's rolling shutter.

In many cameras, the image sensor doesn't capture the entire scene simultaneously. Instead it samples from its pixels row by row. Objects that move between samples may appear distorted across the image.

Here's a paper that describes the typical rolling shutter sampling process and the resulting image geometry.

This article has a lot more details on the rolling shutter effect. Further down the article, when it mentioned (s=1), shows the effect being captured by the above photo:

enter image description here

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  • 9
    See also: What is a rolling shutter? When do I have to be aware of it?
    – Cole Tobin
    Apr 23, 2016 at 17:55
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    If I understood properly, in this case it seems it's column by column, not row by row: i.stack.imgur.com/SPjCX.jpg
    – Oriol
    Apr 23, 2016 at 22:37
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    Most likely this particular picture was taken with a cellphone camera oriented vertically. At least on the iPhone, the rolling shutter goes row-by-row when the phone is held horizontally, and column-by-column when it's held vertically.
    – N. Virgo
    Apr 24, 2016 at 2:44
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    It's also an artifact created by a focal plane shutter when the camera's shutter speed is set higher than its flash sync speed. Most DSLRs (and interchangeable-lens mirrorless cameras, as well as recent film SLRs) use a vertically-travelling focal plane shutter. Since the picture is in "portrait" orientation, that "vertically-travelling" shutter is moving horizontally. Google "focal plane race car" (without the quotes) to see that the effect isn't new, nor does it necessarily have anything to do with pixels (at least not before the silver prints are scanned).
    – Stan Rogers
    Apr 25, 2016 at 2:51
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    There's also this simulation of the effect.
    – Joey
    Apr 25, 2016 at 4:59

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