I've noticed this happening over the last week, intermittently. Instead of seeing an image, you might see a blue image that says Service Unavailable or no image at all.
When I first started experiencing issues, I thought it was on my end and checked the site itself and it wasn't loading at the time. I figured with that the site itself was having issues. Others have mentioned having issues as well.
It could be they are upgrading their server capacity, since more people are using their service.