Greek character caught trio performing by a lake, using images (9)

'greek character caught trio performing by a lake using images' is the definition.
I can't judge whether this definition defines the answer.

'greek character caught trio performing by a lake' is the wordplay.
'greek character' becomes 'pic' (I can't justify this - if you can you should give a lot more credence to this answer).
'caught' means one lot of letters goes inside another.
'performing' indicates an anagram (the letters move around or 'perform').
'by' means one lot of letters go next to another.
'lake' becomes 'L' (geographical abbreviation).
'trio' is an anagram of 'tori'.
'pic' placed within 'tori' is 'pictori'.
'pictori'+'a'+'l'='PICTORIAL'

Can you help me to learn more?