I almost always use a mix of my photos and SketchUp for backgrounds!
When I use my photography, I do a combination of color correction to make it look more stylized, filter gallery styles, and painting over it with Photoshop brushes.
The cover for my first volume was done with that method. I'm a photographer by trade, but this was literally taken on an iPhone while I was waiting for my bus. lol
If I can't get in person access to a background I need, then I use SketchUp to create it. I'm not an expert, so I really just make the most basic shapes to fill in when I draw. I take a screenshot and then use it as my sketch. Here's an example from an upcoming episode! I modeled a waiting room and then used different angles for the scene.
I learned perspective drawing in fundamental art courses in college so I know how to do it, but when it takes me at least 6+ hours to create one background and I have an entire webcomic to write, layout, draw, and color... I don't have time to do it all by hand! Luckily I have a more realistic art style so this process works for me! I hope this is insightful for at least one person.