Material they use regularly captured in picture by a student (8)
I believe the answer is:
physical
'material' is the definition.
(similar in meaning)
'they use regularly captured in picture by a student' is the wordplay.
'regularly captured' means one should take alternating letters (letters taken at regular intervals).
'in' means one lot of letters goes inside another.
'picture' becomes 'pic' (short for picture).
'by' means one lot of letters go next to another.
'student' becomes 'l' (as in L-plates for learner drivers).
'they'+'use'='theyuse'
The alternating letters of 'theyuse' are 'hys'.
'hys' put inside 'pic' is 'physic'.
'physic'+'a'+'l'='PHYSICAL'
(Other definitions for physical that I've seen before include "Having a material existence" , "Tangible or concrete" , "hard work" , "Bodily - material" , "Examination - of the body" .)