One studies images (5)
I believe the answer is:
icons
'images' is the definition.
('icon' can be a synonym of 'image')
'one studies' is the wordplay.
'one' becomes 'i' (Roman numeral).
'studies' becomes 'cons' (conning is a kind of studying).
'i'+'cons'='ICONS'
(Other definitions for icons that I've seen before include "Screen symbols on 4 across" , "Graphic symbols on computer screens" , "Religious or computer images" , "Coins forming pointers on computer screens" , "representative figures?" .)