You know how stock image libraries such as Getty Images are in the habit of asking money for public domain works such as old photographs and illustrations? Boing Boing co-founder Cory Doctorow's new hobby is finding the originals, cleaning up the scans, and making them freely available at Wikimedia.
Once you know the book, it's pretty easy (Getty, Alamy and other public domain pirates are usually pretty good about giving the underlying source in the sell-page for the image). Search for the title at Google Books, Internet Archive library scans, Hathi Trust, NYPL, etc. Locate a hi-rez PDF scan, download, open the page in The Gimp, twiddle the white-balance and rotation, and hey presto! I was already doing this for my own use, and then I'd just delete the image once I'd used it. Finally occurred to me (duh) to put these finished images on Wikimedia Commons once I was done so others wouldn't have to repeat this labor.