I'm sorry - I didn't get this email that there'd been a response! At any rate, I just figured out the problem.
I use smugmug to host my photos. I changed the 'privacy' of the gallery that holds my blog images from Public to Unlisted, and that's when the problem took place. I have two photo blog galleries and the old one has always been set to unlisted (so people browsing my smugmug can't see that gallery), and those blog posts still load fine. But for the NEWER photo blog gallery, when I made the switch, it could no longer import the images to facebook when I linked. I just switched it back, and now everything loads perfectly.
No idea why and don't have time to mess with it. At least I solved the linking problem. I very much appreciate your willingness to help, and no, to clarify, this had absolutely nothing to do with DreamHost.