Concise digit, secure (9)

I believe the answer is:

thumbnail

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'concise digit secure' is the definition.
I can't tell whether this definition defines the answer.

'digit secure' is the wordplay.
'digit' becomes 'thumb' (thumb is a kind of digit).
'secure' becomes 'nail' (both can mean to apprehend or capture).
'thumb'+'nail'='THUMBNAIL'

Can you help me to learn more?

(Other definitions for thumbnail that I've seen before include "Particular sketch" , "Sort of sketch" , "This sketch is short and concise like manual appendage" , "Small sketch" , "Digital process" .)

I've seen this clue in The Guardian.

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