While Photoscape is good, it does not have an twain interface. Basically it takes a file on the computer and lets you edit it. That's great for many things but I found that if you want to get the best possible picture you want to scan it directly into the editing software, edit it and save it. Otherwise you will be saving it as a JPG (and potentially compressing the picture) and then editing a compressed picture and saving it again potentially compressing it some more. It also becomes a two step process, scan, save, edit, save. But for free software it will work great.

You potentially can save the scan in a format that is lossless and that may solve some of the problem. But I use Photoshop Elements. It is a paid-for program (although it doesn't look like it's sold anymore) but I like the tools it provides for acquiring a scan from my Epson scanner, then editing and saving it.