Images aren't too large '500px × 345px (scaled to 100px × 69px)' but there are a lot of them, and to resize all of them takes time.

http://www.websiteoptimization.com/services/analyze/ is a good website with a free service. I'm not sure if its that one or another one, but they give you detailed feedback and analysis so you can see all the results clearly and work on them all.

Good luck!