Dull photo with flowery girl in it (7)
I believe the answer is:
prosaic
'dull' is the definition.
(similar in meaning)
'photo with flowery girl in it' is the wordplay.
'photo' becomes 'pic' (short for picture).
'with flowery girl' becomes 'rosa' (I am not sure about this - if you are sure you should believe this answer much more).
'in it' means one lot of letters goes inside another.
'pic' enclosing 'rosa' is 'PROSAIC'.
(Other definitions for prosaic that I've seen before include "routine" , "Dull - pedestrian" , "Is a crop (anag) - unimaginative" , "Commonplace, unromantic" , "Lacking originality" .)