Gif

We can extract the numbers we see with convert -coalesce brocoli.gif gif.gif command.

To extract numbers, there are a ton of tools out there, but I just used convert -coalesce chal.gif chal.png.

Numbers: 15 13 7 19 15 6 21 14 14 25 12 15 12

Then I used cyberchef for guessing which kind of cipher is it cyberchef

With adding _ to between words and wrapping it in flag format we should get the flag.

Flag: castorsCTF{omg_so_funny_lol}