The guestbook images load very very slowly. Probably because they are quite a bit larger than their preview boxes and also PNG. Simply re-encoding with mozjpeg at 85% (which still looks darn good to my eyes) without rescaling in case you wanted the larger size for retina displays.

    $ ~/git/mozjpeg/cjpeg -quality 85 ge-printer-231017-zenwheel.png  > temp.jpeg
    $ ls -lh temp.jpeg ge-printer-231017-zenwheel.png 
    -rw-r--r-- 1 nemo nemo 439K Oct 18 19:04 ge-printer-231017-zenwheel.png
    -rw-r--r-- 1 nemo nemo  77K Oct 19 09:20 temp.jpeg

Aaand reduced a touch so it still should look good on HD, and cranking up the jpeg compression slightly.

    $ convert ge-printer-231017-zenwheel.png -scale 75% temp_smaller.png
    $ ~/git/mozjpeg/cjpeg -quality 80 temp_smaller.png > temp_smaller.jpeg
    $ ls -lh temp_smaller.png temp_smaller.jpeg
    -rw-r--r-- 1 nemo nemo  41K Oct 19 09:23 temp_smaller.jpeg
    -rw-r--r-- 1 nemo nemo 268K Oct 19 09:22 temp_smaller.png

IMO that would help the page load 10x faster, if you just piped the images through a bit of scaling and jpeg compression.