Last year about this time, I wrote about making miniatures for use in Roll20. In that time, I’ve changed my method, slightly. First, I’ve gone to 200×200 pixels as the standard size for minis, as 100×100 lost too much definition. Large creatures are 300×300 or 400×400 at the largest. Even if it is a giant and you will be clicking and dragging it to a larger size, the resolution is ok, as I use 120 pixels per inch.
The other thing I’ve changed is how I do the white surround. Doing those by hand was not precise enough. Instead, I use the Outline Object plug-in, which is available as part of the Paint.Net Plugins Pack. I set the width at 3 px and the color at white for most things. Sometimes an item is so white (such as a skeletal guard) that it is better to do a 1 px surround in black before doing the white surround. Sometimes, however, that white surround doesn’t work for the image, and then I’ll do a 3 px black surround. Here are some examples of the finished work: