Late last week we did a band width analysis to see where the bandwidth goes. Around 20% of it was spent on THUMBNAILS alone.
We made a change in which anonymous users would see the tiny thumbnails (we store 2 sizes of thumbnails - tiny and large) by default instead of the large ones. Sure enough, bandwidth use went down. We also made the change that the default would be the tiny thumbnails as well.
Now, let's say you want to have the larger thumbnails again, you need to have an account (accounts are free and take only 15 seconds to create) and then set your site optimization for DISPLAY rather than SPEED.
Today, we re-optimized the JPEG previews for display (rather than print). The result is that the thumbnails which used to be 30K on average are now falling to less than 10K even though they look the same. On a typical page with 10 previews, this will save nearly a minute of download time for modem users! Not all the thumbnails have been migrated yet but in the next day or so the process should be completed. Hope the site seems faster.