Images not loading every time on webpage

Hi I run do basic admin on our school webiste: http://www.baldfaceps.com.au/ I have found that after updating to the Catch Kathmandu Pro Theme, often when I load a page not all of the images appear on the site, I just get the alt text for the image. Any ideas on why this might happen. If I reload the page often one image is fixed but another has broken. Any help is appreciated. I only have basic skills.