testimage =
 Plot[{Sin[x], Cos[x]}, {x, 0, Pi}, PlotStyle -> Thickness[0.02],
  Axes -> False]

pts = ImageData[ColorNegate@Binarize@testimage, "Bit"];
g = RegionPlot3D[
    pts[[Sequence @@ Round@{i, j}]] == 1, {i, 1, #1}, {j, 1, #2}, {z,
     0, 20}, PlotPoints -> 100, Mesh -> False, Axes -> False,
    Boxed -> False] & @@ Dimensions[pts]