If its just imgur images then it might be the same issue I had a few years ago.
I(my gaming community) had something similar where imgur images stopped working because they thought we was using them as a host for website's images. (due to the amount of bandwidth they were seeing coming from our domain)
One email to their support and they vetted the site and determined that its a community site and its community members posting their own images and was added to a whitelist.