I use Photo Shop instead most of the time. But it costs more. Here is a before and after pic of Lucee in Photo Shop. It has a highlight/shadow feature. So the worst pic can be fixed. This isn't a great pic, but one that shows how you can fix a good one if it is too dark.
Katz
This is Lucee in Ash's bed, watching Kelcee. WAY too dark, no flash.

And here she is using the shadow/highlight feature. some programs have lighten features, but they lighten the over all pic, and you get a washed out photo, not just the shadow parts brought lighter..