I'm having the same issue with downloading the expedition pictures. Right-click and save on an un-expanded image doesn't work either. I wonder if it's some kind of copyright protection.
The first possibility is that they came that way.
A second is that it is meant to make the page load faster.
"Why Slice? How and Why to Slice Web Images" is just one of many articles that our friend, Google, turns up.
I can view the images as a whole on my computer by clicking on them.
If I felt the need, I could capture what I see on the screen by pressing the "PrtScn" button on my keyboard, and then editing the screen capture in any number of free programs that I use for such purposes. (I use a PC, FWIW; Mac and Linux users have their own techniques available to them, I'm sure.)
I don't feel the need to attribute any dark motives to Pat Thrasher or to TIGHAR. The pictures are quite lovely, and they help to tell the story of the expedition.