One captured is held at arm’s length? (6)

I believe the answer is:

selfie

I'm a little stuck... Click here to teach me more about this clue!

'one' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for selfie that I've seen before include "21 [PHOTO]" , "Personal photo" .)

I've seen this clue in The Independent.

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