A recent post on Germanic script ("Those Were Not Diacritics--They Were Wiggles") included an image from Ernest Thode's German-English Genealogical Dictionary.
It also included a citation and a notation that the image was used with Thode's permission. I'm not even going to concern myself with whether or not the size of my image would have qualified under "fair use." My policy here is to ask permission before using any image anyone else has created.
It's easier that way--and creates fewer problems.
It's also the polite, ethical, and responsible thing to do. Sometimes just because something is legal does not mean that it should be done.
So if you see a hand drawn image as a blog post illustration that looks like it's been drawn by a child--rest assured I made it. No one usually wants to take credit for those.