From the beginning, mankind was told not to make idols and displace their reverence for God by a physical image or talisman. It has been enshrined in the Ten Commandments ("Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth: Thou shalt not bow down thyself to them, nor serve them:" (Ex. 20: 4-5.) The commandment extends to the "likeness of anything that is in heaven" and would include the Lord.
The images I have seen of Him are for the most part inaccurate. The reason we don't have accurate pictures is in all likelihood related to the fact that those who come to see Him would understand the importance of avoiding idols and would question the wisdom of recreating an image of Him that might be used by others to displace their attention and worship.
What is appropriate is to affirm that He is real, that He lives, that He has been resurrected from the dead, and that He came, sacrificed and rose because of His role as the Savior and Redeemer of mankind. I've written as much as I've been asked to write about Him by way of testimony in the Appendix to Eighteen Verses, in Come, Let Us Adore Him, and a brief physical description in Nephi's Isaiah. However, the brief physical description is not enough from which to reconstruct an image. It merely refers to some of His physical attributes and then tie them to the scriptural accounts to show why the narrative in the New Testament would read as it does.
The most important understanding of Christ is tied to what He suffered in Gethsemene. D&C 19: 16-20 and my testimony about Gethsemene are both useful in understanding what He went through and what role our own actions will play in obtaining the benefits of His Atonement.