In the Discord server, send a message containing the text `:emote:` to post the emoji.
Using whichever method your device supports (browser/app/desktop), download the image. It's easiest to do in the browser with Inspect Element.
Then using an Image to Binary converter such as [this](https://www.dcode.fr/binary-image) one, first make sure to set "Original Size" and not "Reduced Size".
Then convert the image to binary.
You may now use whichever Binary to Text converter you prefer (such as [this](https://codebeautify.org/binary-to-text) one), and you will get the flag:
`uiuctf{staring_at_pixels_is_fun}`