images not showing up – randomly!

Hey all,

on my website: http://www.jerusalemphotoinstitute.com, i have images randomly no showing up. sometimes they do, most times they do not.

i.e. like the front page image, and under this url:

http://jerusalemphotoinstitute.com/studenttestimonials/

Also, sometimes i upload images to the media library, and i see grey squares instead of an image.

Can anyone help me figure out whats going on?

Thanks.