It really depends. Some posts are very old, and if their images were attached to a posting on this board, they can be lost in a software upgrade. If someone has hosted the image themselves, and linked it to their post, then its up to them to keep the image available, and they and their hosting company may keep it up for as long or as short a time as they feel like it. If a posting contains nothing but an image that's been lost, and no typed question, and has no answer except, "Yes, that's correct" or "Try harder," then I tend to delete the posting when I notice it to remove clutter. But any sort of discussion, even if the image is lost, is worth keeping.
Or do you mean you can't see Latex equations?