This piece of software called OmNomNom works with OpenSCAD to turn 2D images into 3D models. It’s literally a drag-and-drop process that renders almost instantly.
Here the example is a QR code, which is perfect for the software since it’s a well-defined black and white outline in the source image. But the video after the break shows several other examples that don’t rely on this simplicity. For instance, the Superman logo, which uses four different colors, is converted quite easily. There’s also a depth map of [Beethoven's] bust that is converted into a 3D object. The same technique can be used to create terrain from topographic source images.
Once the file has been converted to a model it can still be tweaked like normal. This allows you to customize size and depth to suit your needs. This is where OpenSCD comes into play, but if you don’t use that program you can still export an STL file directly from OmNomNom for use on your 3D printer.