Photograph of empty measure, say (8)
I believe the answer is:
hologram
'photograph' is the definition.
(hologram is a kind of photograph)
'of empty measure say' is the wordplay.
I cannot really see how this works, but
'of' could be 'o' and 'o' is located in the answer.
'empty' could be 'o' and 'o' is located in the answer.
'measure' could be 'gram' (gram is a kind of measure) and 'gram' is present in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for hologram that I've seen before include "Three-dimensional image or representation" , "Three D image" , "3-D image" , "Three-D laser image" , "Three-dimensional image created on film" .)