Do you see Albert Einstein or Marilyn Monroe in this image?
You should see both. If you never see Einstein, chances are you need glasses.
According to the folks over at ASAP Science, who made a video showing how it works, the image above is a hybrid image. It’s a combination of two separate photographs — one of Marilyn Monroe and one of Albert Einstein.
The reason the image appears to transform is because one image (Einstein) is made up of super dense pixels, making his details, like his mustache and wrinkles, pop, while the other image (Marilyn) is made up of far fewer pixels, causing only her basic features to show up.
Here’s the image of Marilyn. You can easily make out her face shape and basic facial features, but not much else:
And here’s the image of Einstein. You can clearly see the fine details of Einstein’s face, like his mustache and wrinkles:
When you see one image, it clouds out the other.
Problem is, if you can’t make out Einstein’s details, you’ll never see him in the picture.
As the GIF gets bigger, you can see its details more clearly (just as you would if you were walking closer and closer to a static, unmoving image). Someone looking at the full-size GIF should see Einstein, because the more vague, general information represented by the Marilyn image (the shape of her face and features) should fade once they can make out the sharp details (mustache, wrinkles, etc.) in the Einstein image. You can read more about the details of this concept, known as spatial resolution, here.
Alas, if Marilyn never transformed into Einstein, it might be time to make an appointment with your eye doctor.