Possibly mark door of place where photos are developed (8)
I believe the answer is:
darkroom
'place where photos are developed' is the definition.
I can't judge whether this definition defines the answer.
'possibly mark door' is the wordplay.
'possibly' indicates an anagram.
'mark'+'door'='markdoor'
'markdoor' anagrammed gives 'DARKROOM'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for darkroom that I've seen before include "Place to develop films" , "Gloomy place where photos are processed" , "Film-developing cubicle" , "development area" , "developing area" .)