I was able to download SOME of my cover photos, using Chrome and directions similar to what were given by Isidro.(Thanks!)? But on others I got the error message cited:"We are sorry, you can not display images hosted by Yahoo! Groups on non Yahoo! Groups pages" .
?For whatever reason I had no success using Firefox and also tried Internet Explorer with no success. I consistently got the error, but it may have been due to the particular groups for which I was attempting to download the covers, rather than the particular browser?
The string of text you are looking for in the goobledygook starts with http and ends with cover.jpg
I did the right click on the photo (or the space where the photo should have been), then selected inspect element or similar, then a chunk of gobbledygook was highlighted. Then I highlighted the chunk directly above this which included the cover.jpg link. I right clicked on it and selected copy > outerHTML or similar , then pasted this into the address bar of the browser, where I used the right and left arrows to help in deleting unwanted text around the "http...cover.jpg" string. The string is actually in there twice.
Since the procedure worked SOMETIMES for me, I may retry periodically to see if Yahoo eventually allows me to display and save the images. Or does anyone have other suggestions? Linda N