I most often read books from scans rather than paper, I also highly preferred it to be in the form of batch of jpgs/pngs rather than in a single pdf since it can give me a very fast overview of the whole book. It will also allow me to quickly open multiple separate pages at once to quickly compare.
The problem is when I want to quickly underline something. This isn't a thing that the Windows Image Viewer can do. So can anyone here recommend a good lightweight image viewer with simple editing features, at least some kind of simple pen tool? Any help is highly appreciated.