First off, here’s Luther (described by Heiko Olbermann, quoted by RSC):
With regard to Luther’s judgment on images, we are not in the dark. In his report to his confidant Nikolaus Hausmann on the situation he found in Wittenberg, he was unambiguous: “Damno imagines.” The elimination of images, however, should be brought about by means of a consensus grounded in the faith. As far as the intended action goes, Luther’s posture was in 1522 appears no different from the position Erasmus had counseled six years earlier—images should be tolerated until they can be removed sine tumultu. On March 17, having just arrived from the Wartburg, he summarized his strategy on images this way: “They would fall of themselves if people were taught and knew that before God symbols are nothing.
53:24 — Calvin’s view was to wean the people away from the idolatrous use of images and icons in Rome. But it was not an absolute principial objection; he thought it was a temporary, prudential need to change the worship culture of the church from the idolatry that was rampant in Rome, and the Roman use of images, Bob, you know that, and that’s why I’m saying, if we’re going to be Calvinistic, if you’re going to follow Calvin on this point, Calvin theoretically allowed for the use of images — prudentially — after a moratorium to liberate a generation of people from that stuff.
So Luther’s Reformation was temporarily for images, with an end goal of eliminating them, but Calvin’s Reformation was temporarily against images, until they could be allowed in appropriate uses?
Personally, although I think Sproul’s words well describe the actual situation of the early Reformed churches wrt idolatrous Rome, I have never seen any writings that would back up this actually being Calvin’s documented position. If there are any, I wish I knew about them three years ago, they would have come in really handy!