indistinguishable

/ˌɪndɪˈstɪŋɡwɪʃəbəl/
adjective
  1. Impossible to tell apart; so similar that one cannot be distinguished from another.
    • His voice on the phone was almost indistinguishable from his brother's.
    • In the fog, the shapes of the buildings were indistinguishable.
    • The two paintings were indistinguishable to the untrained eye.