Thanks everyone. Since I have had weird permission issues before, it was the first thing to check, and that was not the issue.
I ended up with re-uploading all the image files to remedy this problem. Took me all night, tho.
I then realized I _did_ change something yesterday which I totally forgot about it. I added another instance of IMAGE SIZE under Site Config > Image. This must have done something bad. Is this a bug that I should report?