If you ARE a Linux geek than you probably use GIMP, which is open source photo editing software.
There is a plug-in called Cross-stitchify v2.1 that you can use to turn any photo into a cross stitch image. Fun!
It’s pretty easy to make a cross stitch pattern out of a photo using Photoshop too. Here is a great tutorial for using Photoshop to make a cross stitch pattern.