I work IT, so I can speak to this directly. First, yes, they COULD if they really wanted to check every single website you are viewing. However, most companies never bother, because the volume of web traffic is so large they would spend a week just analyzing every single link everyone has gone to in a single hour to figure out what is bad and what is legitimate. They might institute some sort of filtering or blocking system to weed out traffic by specific tags, like porn, but since imgur isn't necessarily porn it won't get blocked (not all the time... our filters at work are good enough that they do sometimes pick up the tags people apply to a photo or the words they use to describe it and block the content anyways). There's just not enough resources to handle checking every single users web useage.

The only time most IT departments take an interest in what a specific user is doing is if there is a complaint or a reason given to do so (ie, performance problems, too much time on internet, etc.). So, really... you're probably pretty safe, don't sweat it.