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]