The background is an altered paper, made by saturating magazine pages with a solvent liquid called CitraSolv, which completely dissolves the printing ink and creates lovely patterns and the characteristic 'bubble' effect which you can see here (if you look closely, you can see some of the text from the magazine page, which is still visible.)
I scanned one of those papers, and also scanned a pencil portrait I had done, and then combined them using Photoshop. I chose a paper background that I felt was most compatible with the portrait, so they feel like they go together. There is some re-sizing and manipulation to make the two elements 'fit' as one piece of art.
I hope that helps to explain the process.