At one point, I think that recently uploaded images were showing up in my news feed. They aren't now, and I'm wondering how I can make them show up again?

Ahh, I found it. I had turned off "CombiNews" in options->plugins->zenpage

That is what the feed is for. There are different options for the image feeds. Please review the option description. Zenphoto is file system based so just uploading does not necessarily add images as the feed is take from the database, on "discovery" so to speak.

Ok, now on to my real question... How can I print a news page with ONLY image articles?

I am not sure what you mean. Image entries are not really articles, they are just mixed inbetween the real articles as if they were articles. Their "singe article page" is the image page (everything else would be double content).

If you only want to have image entries on your news loop, don't write normal articles.