That’s the text that shows up in the composer when you upload an image so hopefully won’t catch anyone out as it will be displayed there when you create your post:
People can edit it out and replace it with something else (hopefully something more descriptive if they are kind and thoughtful people 
) from in the composer or there’s a nifty shortcut on the Preview that accomplishes the same thing:
It also shows up in the search and oneboxes, etc so there’s no practical way of obscuring it.