The flag was written on the diagonal of an image, then a swirl filter had been applied to the image. Afterwards, the image had been split into 4 segments, and each segment had another swirl applied to it. Manually de-swirling each image, stitching them together int a large image, then de-swirling that, gives this slightly readable image. Note that it's not possible to recover the original image 100%, because the swirl operation is lossy. Each de-swirl was about 270 degrees.
![league.png](https://i.imgur.com/2dNrgvq.png)
We had trouble figuring out the case of each letter, but when the flag was made case-insensitive we managed to solve it.
`rtcp{y3p_n0th1ng_to_s33_h3re}`