I have found two places where Sproul deals with this subject. The first is in Essential Truths of the Christian Faith, v2, where he expresses concern about the risks of "wrong images":
I can't say for sure that to depict the human nature of Jesus is a violation of the second commandment. But I'm not sure this is wise because it could communicate an image to people that is inaccurate. The Solomon's head of Christ, as beautiful as it is, has communicated to generations of people an effeminate Jesus who is somehow less than strong. I would rather communicate nothing artistically about how Jesus looked than put wrong images in people's minds.
The second is in his teaching series, "Recovering the Beauty of the Arts," particularly lecture 7, on images. Here he focuses on why he is not categorically opposed to these images:
I say to my friends who prohibit it, let's get over our gnosticism. When we're painting images of Jesus, we're recalling the human Jesus just as we do the apostles. That's part of nature, and we're not trying to capture the divine nature in those representations.
Jesus didn't say before he left to his disciples now I want you to blot out of your memory any recollection of what I look like. Because obviously they couldn't block that out of their recollection, and there was nothing wrong with Jesus manifesting himself with the likeness of human flesh.
I don't see anything that would prohibit that from being reproduced, artistic creativity, in the life of the church. But obviously any use of art in church runs the risk of degenerating into idolatry. But I also think that the cure for abuse is not disuse. Historically we have God adorning his presence with the beautiful, and I think that he has placed a pattern there, a principle there, that remains forever. [starting around 22:30]
The context for the last statement comes from elsewhere in the lecture, where Sproul defends the use of art more generally on the basis of God's direct command to artisans to fashion the ark of the covenant with cherubim, as well as other artistic elements for use in the tabernacle and the temple.
Within the Reformed tradition more broadly, many have written defenses of the didactic use of images of Jesus. But perhaps the defense most relevant to the question is found in the 1981 RPCES Synod report, pages 89–107. It deals with both the historical context and exegesis of Exodus 20, and concludes:
(1) Contrary to L.C. 109, we do not find pictures of Christ prohibited by the Second Commandment.
(2) In regard to the Second Commandment, we do find Scripture urging caution in making portraits of Christ, that their purpose not be primarily to render a "likeness," to show what Christ looked like.
(3) That other pictures of Christ, depicting events from His earthly ministry, are permissible. (103)
The relevance of the RPCES report is particularly heightened because it was written just a year before the RPCES joined the PCA, the denomination in which R. C. Sproul ministered. Of course, that's not to say that he had identical views as those who wrote the report, but it at least provides additional theological discussion from Sproul's peers on this subject.
