Most of us who toil away at webcomics have day jobs. This means that, frankly, sometimes we're pressed for time and shortcuts must be taken to make our scheduled updates. One of the advantages of the digital age though is there are some easy shortcuts that come easily - like reusing backgrounds. Comic artists have been reusing backgrounds since, like, forever - but I like to go a bit further by building reusable "Sets" which also include foreground elements and lighting. Since I'm using these techniques heavily in The Chronicles of Crosarth and UnCONventional, I thought I'd walk through a simple example of how I do this.
The set we're going to build is Lynn and Megan's bedroom. We start out with a basic background which is just a black and white, high contrast photo of a window in this case.
Our other main element is Lynn sitting up in bed. This element is actually two that I flattened (Lynn is separate from the bed itself), but for simplicity I'll present it as one element here.
The obvious first step is to combine the two. These are set up as two different layers in my graphics program (GIMP in my case, but almost every major graphics editor you'd want to use for this sort of project supports layers), because we're actually going to insert something between them. Also, we want to be able to swap Lynn out later for other things so we can reuse our work (which is sort of the whole point).
As the room is supposed to be dark, the first thing we're going to do is darken the background. I do this by creating a translucent black layer in between. The background should be darker than the foreground in a dark room scene just because we're going to need to see the foreground in the comic more clearly.
Our last layer is foreground lighting. In this case, we've creating a translucent layer on top of the foreground. Rather than being solid though, we want to create the illusion of a light source. To do this, you just need to create a gradient which fades to transparent towards whatever your light source is.
Once that's done, you can do other things, like swap out different foreground elements without changing the lighting.
This means you don't need to recreate the entire image just to move where a character is in the frame. Likewise, you can adjust the lighting on the same frame.
In any case, I hope that sort of made sense to you. This was a simple example, and I do much more complicated ones for sets I'll reuse for multiple strips. Lighting can play a major effect as well - for example this image and this image are generated from the same virtual set. Admittedly, the first one is visually identical to the original photo.
It's a mix of my photos and some public domain shots with some adjustments made to most of them. Most are in Eau Claire, but some (like the Marshall Hotel, which I didn't want to look like any of the hotels in Eau Claire) come from other places (in that case, the Lafayette Indiana Holiday Inn). Like, Unagi Con's hotel was the recently defunct Stevens Point Ramada. I don't match Eau Claire geography exactly, as Eau De Puanteur is supposed to be a different town (and Eau Claire DOES exist in this reality), but visually I want Eau De Puanteur to have the same kind of look.