What does it mean if a guy likes your profile picture?

Here's a question my friends and I are always wondering: If a guy that you don't know extremely well "likes" your profile picture on Facebook, what does this mean?
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Keep in mind: Under 18, so try to post relevant answers to that age category ahah.
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Guys, do you like random girls' profile pictures or do you have an intention behind every "like"?
What does it mean if a guy likes your profile picture?
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