I used the wrong choice of words, sorry Jake. I don't know the right term, but I can offer an example.
In /styles/xenforo there is the XenForo.png file. If I remove or rename that file, when I log into the ACP I see the text "XenForo Logo" where the image normally appears. That is the effect I desire. Text that describes the image, which also takes the image's place in case it does not load for any reason.