Here's a method based on creating a `MeshRegion` from the text:

    text = Style[HoldForm @ Sum[x^2, {x, 0, 10}], 100, Bold];    
    graphics = First[text ~ExportString~ "PDF" ~ImportString~ "PDF"];    
    region = DiscretizeGraphics[graphics, MaxCellMeasure -> 5];    
    image = ExampleData[{"ColorTexture", "Kingwood"}];
    
    RegionPlot[region, Frame -> False, BoundaryStyle -> Black, PlotStyle -> Texture[image]]

![enter image description here][1]

Or in 3D...

    Plot3D[1, {x, y} ∈ region,
     PlotStyle -> Texture[image],
     Extrusion -> 10, BoxRatios -> Automatic,
     Mesh -> False, Boxed -> False, Axes -> False]

![enter image description here][2]

Tiling
======

To tile the image you can use `TextureCoordinateFunction`, e.g:

    RegionPlot[region, Frame -> False, BoundaryStyle -> Black, 
     PlotStyle -> Texture[image],
     TextureCoordinateFunction -> ({5 #1, 5 #2} &)]
![enter image description here][3]


  [1]: https://i.sstatic.net/hP7xb.png
  [2]: https://i.sstatic.net/jx4cH.png
  [3]: https://i.sstatic.net/1LwBz.png