Pictures of the centre of the Earth? (3)
I believe the answer is:
art
'pictures' is the definition.
'the centre of the earth?' is the wordplay.
'the centre of' means to look at the middle letters.
The centre of 'earth' is 'ART'.
'of' acts as a link.
(Other definitions for art that I've seen before include "The works of Alma-Tadema" , "Cunning" , "Trickery" , "Beautiful or significant products of human creativity" , "Skill, knack" .)