Septentrion_P said:
I just paste portrait images together. I just don't want boring filler space. White is especially hard on my eyes.
I agree, "white space" is boring and does not lend itself well to a screen background image,but it is not always easy to find images that complement each other like bookends.

Some extension ideas that I think work well:
  • Background extensions do not have to be boring white filler space, post #103106 is a nice example of a simple but aesthetic background extension.
  • Zoom layers such as post #162178 also nicely fill that "boring white space"
  • Bookends if you can find complimentary portrait images, for example post #234910 or post #235313
Here is a request :)
http://www.pixiv.net/member_illust.php?mode=medium&illust_id=39420633