I had the same problem, then downloaded keiths ipod photo reader,
http://keithwiley.com/software/keithsIPodPhotoReader.shtml for free and it helped me open the files. So download keiths, then hit load .ithmb file, and select one of the 4 .ithmb files you have, and it'll show you a little image on the left of what they'll look like when opened, click on all the decoding image buttons to see which fits best, and once you find it hit open all images on file, and all the images will open. Repeat with all the .ithmb files.
Don't worry all your photos should be contained in the 4 .ithmb files you have.
Hope this helped