+1 for D.

(A) with merely being a photographer

(B) as being a photographer merely

(C) for being merely a photographer

(D) as a mere photographer --> Correct, rectifies idiom error, "Dismissed as something"

(E) merely for being a photographer

Hence, D.
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All options but D have a repetition of the verb to be. Verb tense of being is usually really awkward and should be avoided if possible.

Concept tested : Idioms

Idiom tested : dismissed as

Ans : D
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Imo D.
A is wrong as it has with. The correct idiom is dismissed as.
Being is also superfluous here.
B is just horrible on meaning front. It suggests that he should be the photographer for some more people other than for visually impaired.
C for is not correct in this context. When some noun is used such as bad behaviour than we can use for.
For example, He is dismissed for his bad behaviour.
D correct.
E Meaning is not correct as it implies that he is dismissed for merely being a photographer for visually impaired and he should have been some more role.

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Here Correct Idiomatic usage is "Dismissed as"

All other Options are eliminated for the highlighted portions