as salam alaikum
the evidences that some people brought forth to say that the picture of Imam 'Ali, peace be upon him, as seen in certain areas, is the actual images of him, like the descripition of general Imam's features in some books or the vision of the Imam in a dream, are insufficient to establish the reliability of such claim.
Also, considering the subjectivity of such type of art, some people have found such pictures disrespectful to the Imam himself. In any case, it wouldn't be correct to attribute such images to him.
With prayers for your success.