Making an image appear scanned

Looking at the image on the right, it is clear that it was computer generated. Real printed material is never this clean. If you want to make the image appear like it was printed out and then a photographed or scanned, so some dirt needs to be added. Also when printing, sometimes the different color components can be a bit offset from each other, so let's mimic that too. The colors should be done first, because the dirt isn't supposed to be offset.

To create an appearance that the colors were printed separately with poor accuracy, first split each RGB color channel by using "image > mode > decompose" from the menu. Select that you want each color to be its own layer. After clicking OK you will get a new image, one layer per color component. Now you may get an urge to use the move tool to move these layers around, but it would have no effect at all, because when the image is recomposed the positions of the layers are ignored. Instead you have to go inside the layers, select an area and move it so that it actually moves inside the layer.

If you are unsure how to do this, begin by pressing CTRL-L to view the layers, then single out one layer by turning off the eye button from the two others ones. On this layer use the selection tool to select the whole image, press CTRL-C to copy it, CTRL-V to paste it, then move the pasted selection very slightly to some direction. Do this again on another layer, so that you have two layers with the contents shifted a bit.

Now select "image > mode > compose" to recompose the image. You should get an image where the colors are off slightly from each other (if the colors look completely different, be sure you didn't move the layers around in the layer list before composing). Now we can add some dirt into this combined image. Use "filters > noise > scatter rgb" to do this, then "filters > blur > gaussian blur" with a small value like two pixels, and you should end up with an image similar to the one on the left.
Really does look quite like someone actually printed it out and then snapped an image of it with a digital camera, doesn't it?