Well who else but Amazon.com, right? Well not exactly!
Amazon seems to discourage freeloading of their images by placing obtrusive "Search Inside this Book" arrows or watermarking them with "COPYRIGHT MATERIAL" so that freeloaders like me won't link directly to the image, or even rehost the image file since they appear with defacement gratis.
Well, after playing around with their hyperlink code, it appears that I found the right combo which displays the image I need in the right size for my page.
Here is an example:
<img src="http://images.amazon.com/images/P/XXXXXXXXXX.01._SCMZZZZZZZ_.jpg" />
The first part in blue characters should not be changed. The part in red must be replaced with the ASIN of the Amazon item you are linking to, which should be a 10-character string (the ASIN of a particular item can be found by looking at that items page on Amazon.com.)
As I finished writing about this
To repeat what the author of that page said -- don't be an ungracious leech; if you're going to link to their hosted images, at least link to the sales page so that Amazon can make a buck off of it.