As I've done for years on the Quoom site, I right click on the image and usually a window pops up with "Save Image." But now, nothing happens. But I'm going to go take a look at Quoom's site, since what you say about stopping image download is relevant.
UPDATE: Well, I found a work-around, but the people running the site now seemed to have done their best to conceal it. What you do is to get the image you want to save displayed, then hold down the SHIFT key and right click the image. You'll get a small window with "Save Image" as one of the choices. The only downside is that the filename of every image defaults to "canvas.png," so you have to manually select a filename and keep track of the increments yourself.
I did a few tests in one of Quoom's later, incomplete works named The End of the Witch Queens. I made a folder called "1" for the first set of drawings and named them "queen 1.1," "queen 1.2," etc. Pain in the butt but it works. So I'll probably stay a member long enough to make sure I've got all the imagery he's posted lately.