Polish up a picture of the river (7)

I believe the answer is:

rubicon

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'the river' is the definition.
(I've seen this before)

'polish up a picture' is the wordplay.
'polish up' becomes 'rub' (polish meaning rub to make shiny. I am not sure about the 'up' bit.**).
'a picture' becomes 'icon' (icon is a kind of picture).
'rub'+'icon'='RUBICON'

'of' is the link.

Can you help me to learn more?

(Other definitions for rubicon that I've seen before include "Stream in north Italy that Julius Caesar crossed in 49 BC" , "Caesar's fateful river" , "Stream in northern Italy" , "Caesar got over this" , "River, point of no return" .)

I've seen this clue in the Evening Standard.

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