TL;DR version because accidentally didn't post earlier and lost it. I felt this was important to make a post about where you wont have to see it in every single image that I may post in the future, plus will save me time.

Old pieces mostly 2017 and earlier sometimes use stock photos for backgrounds from this site:
https://www.pexels.com/photo-license/

Despite this I try to make the character the main focus of the piece.

If you pay me for a background through commission I will draw it myself and not use a stock photo.
If you pay me and want me to use photo bashing to make the background I will do that if requested.
At my own disgression I will use 3D modeling software to help me make the background.
Reference images don't count 

More info on photo bashing: https://www.youtube.com/watch?v=_LxJ2fy-0Zg