You can do it, by going to 'More Options', and put the Max Font Size to 0 px. Whatever you type won't show up. This is also a trick if you want to repost an image that already has text on it. You can either try to enter exactly the same text, and position the text exactly on top of the text that was there, or enter exactly the same text and put the Max Font Size to 0px, so it doesn't show up. Entering text is important regardless, not so much for comments, but for memes, because the description is indexed for search engines.
Caption this Meme
