Are there any eyewitness descriptions of the physical appearance of Jesus?
Unfortunately for many theologians, historians, and artists alike, we don't have many descriptions of what Jesus of Nazareth looked like. The descriptions we do have (in Scripture) are quite vague and tells us more about the metaphorical value of his appearance than what Jesus may have actually looked like.
There are a few descriptions of Jesus' physical form in the Bible. For example, in the passages of Isaiah, Jesus is described as being a fairly ordinary looking man. At least, he was not beautiful or especially attractive in a way that drew a lot of attention to him. While this doesn't offer us many concrete details about the appearance of Jesus--only that he looked like a typical Galilean--it does give us a chance for interpretation. Why might it have been important for Jesus to look like any other "Average Joe?" It emphasizes his humanness and makes him more relatable across space and throughout time.
In the book of Revelations, Jesus is described in the form he attained after rising from the dead. He is described as having white hair and that his feet and eyes were glowing like fire. The rest of the description deals with his adornment.
This article from the BBC explores some questions about what was likely to have been or not been a part of Jesus' appearance based on his actions. For example, would it have been practical for a carpenter to keep his hair so long? They also include a photo of the facial reconstruction of a skull found from about the time and place Jesus lived.