Is there a software that would let me put a wallpaper on only, like 9/10th of the screen (horizontally)?
I have the taskbar on the side and I don't want wallpaper underneath it.
I'm on Windows 8. It could be freeware or paid.
You can take your, candidate, wallpaper and add a bar, of whichever colour you like but probably black or white, of the desired proportion, that occupies the first/last 10% of the image, either overwriting that much or expanding the image size by that much.
You can do this by hand with any image editor, gimp is free & great, or with a little work tools such as imagemagik, (also free), will let you write a batch file that will take one image as an input and generate your new one for you.