How do I hide img src image using css?

I’m using FeedWordPress for a blog feed. There’s an ugly “Add Comment” image link at the end of each post that I can’t seem to turn off. I’d be satisfied with display: none, opacity: 0, or something like that. I’ve only got the img src to work with. Is it possible to define an image class and assign it to the img src using only CSS? How, exactly, would I do that?

Thank you,
Lisa