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This morning on twitter there was a tweet with the text "click on this picture". When picture is clicked, it's opened in wider viewer, but looks completely different.

I tried to analyze this picture in ACDSee, and I also tried uploading on Facebook, but it's happening only when embedded on twitter. I don't have much knowledge about graphics so please explain this to me. Why does this PNG image change only when clicked on Twitter?

Screenshots (left = before clicking; right = after clicking):

Before clicking After clicking

Here's the original picture.

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Try dragging the guy in front of the stars, most browsers will then show you that this is a transparent png by rendering it with a gray/white background while dragging – PlasmaHH Aug 8 '14 at 10:36
See also this answer to another question, where I describe how pictures like this work and how to create them. – Ilmari Karonen Aug 8 '14 at 13:44
up vote 23 down vote accepted

The picture doesn't change. The background color of the page does.

It's a transparent PNG. The whites are not visible on a white background. The blacks aren't visible on black background.

The normal post is on white. The modal view is on black.

If you change the background color...

Black White

share|improve this answer
Also if you use another background colour, such as dark grey, you can see both images at once. – deltab Aug 8 '14 at 14:15

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