In the Bat Mobile (http://www.thingiverse.com/thing:4453) I used a 2D image, converted to a single line which was meant to be drawn by the unicorn pen plotter. I did not plot the image, but printed the image in plastic with 3-5 layers to give it some strength. It is possible to print images like that directly on paper which gives a nice effect for postcards.
Attached a picture of an example how a thin plastic image is printed on a postcard.

Images can be printed separately and glued on paper, or printed directly on the paper used as a card. Make sure the first layer is squished a bit. Attached is the gcode file of the pumpkin.

IMPORTANT: Before you print the pumpkin from the gcode file you must edit it. The gcode file is created using scripts to convert from an svg to an gcode file directly. The layer thickness is set to 0.3 mm, but parameters like the initial warm up procedure, possible homing, stopping of the heater at the end etc. are NOT included since this is different for each style of printer and for each material. I use a repstrap printer with makerbot electronics and firmware and PLA. Editing is not difficult. Compare a gcode file you have used successfully for some other print and use the header and tail(!) from that to complete the attached gcode file.
The coordinates used in the file are all positive between 0 and 70. Make sure your initial zero position allows for that.