To start, you'll need a 3D modeling program (i used Rhino), Adobe Illustrator, and somewhere to 3D print your model (I used my makerbot). You can also download my .stl file if you want to save some time and skip to the printing step.
Step 1: Trace Image
Set up your vector image
To make the 3D model for your cookie cutters, first you'll need to trace a vector outline of the Tardis. I used Adobe Illustrator but you can also trace your image in your 3D modeling program.
Find a view that you like online and paste it into a layer in Illustrator. Lock the layer so it doesn't get in your way while tracing. Make a new layer and use the pen tool to outline it the image. Make sure when you finish back where you started so the whole outline is one closed shape. Otherwise you'll run into trouble in the 3D modeling step. Try to scale your file to the size you want your cookies now so you'll have the correctly sized vectors to base your model off of. I made my Tardis about 4" tall (about the size of a non-transdimensional cookie). Save your file as .ai (so that you can import it into rhino)
Step 2: Turn Your Vector Into a 3D Model
Next, import your .ai file into your 3D modeling program (I'll be using Rhino so other programs might have different names for the same commands).
Use the "offset" command to offset your vector about .075" to the outside of your drawing. That way when you cut your cookies, they'll be the same shape as your drawing and not the shape of your offset path.
Next, select both paths and use the "extrudeCrv" command to extrude both paths at once. I recommend making the extrusion about .5" In Rhino, It should automatically close the extruded surfaces into one closed solid.
Export the solid to a .stl file for printing.
Step 3: PRINT
If you're using a makerbot, you can open your .STL directly in Makerware to print.
You can also use a service like Shapeways or Ponoko.
After you have your cookie cutters, use them as you would use any other cookie cutter, but be careful. They only work on blue cookies.