I see. The trick is to be out of focus. By the way, nice figures you have!You can use Photoshop, but I find it too tedious (don't have the patience).
Image quality of the background isn't an issue as it will usually be out of focus. You do have to make sure you're not catching too much glare from the TV-screen. I did notice that when using too low a resolution photo you can sometimes see these raster lines in the background.
I confess that I like to edit in photoshop. You can even remove the base support from the actions and put expressions on them!You can use Photoshop, but I find it too tedious (don't have the patience).
But this one has heavy rastering on the actual same background as the phot above. I believe it's because the zoomed-in background image I used is too small in combination with the distance of the camera to the screen. I haven't figured it out. To be honest it's not important enough to me. Most of the time the photo's turn out fine: