The strangeness of my brain

My alternate history manuscript is the first time I've used real historical figures as major characters. People famous enough to show up in my story tended to have their portraits painted, some of them so frequently that I swear if you brought them forward in time and dressed them in modern attire I'd immediately recognize them walking down the street. But the funny thing about knowing these people mostly from portraits is that every once in awhile my mental image of the scene will switch from human beings moving through a three-dimensional landscape into paintings done in the style of the era, and I have the hardest time coaxing my imagination back into 3-D.