Up close, your eyes can see tiny lines, so the sketchy wins.
Far away, those lines get too small for your eyes to see. Only the big blurry shapes are left, so the wins.
Scientists call this spatial frequency: how big or tiny the details in a picture are.
Why does this work?
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Your eyes have two jobs
Part of your vision spots big blurry shapes. Another part picks up tiny sharp details.
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Distance shrinks details
When you walk away, everything looks smaller. Tiny lines get so small your eyes can’t see them anymore.
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A famous trick
Scientists mixed Albert Einstein and Marilyn Monroe this way. Up close you see Einstein; from across the room, Monroe.
Source: Oliva A, Torralba A, Schyns PG. Hybrid images. ACM Transactions on Graphics 2006. doi:10.1145/1141911.1141919
Watch: Spatial frequencies and the Einstein/Monroe illusion (ok science)