As the question gives us a mega link so we download that
file/directory and we get a file called "AGT.png".
So we examine the file first with opening that file but that file does not open so examine file we use
file command
file AGT.png
Now file shows jpeg format then we change the extension then open and voila it opened but nothing interesting
so we check for any metadata with identify
command in linux
identify -verbose AGT.jpeg
But nothing so we check for any hidden files/directory with binwalk.
binwalk AGT.jpeg
We see some folder hidden inside so we extract these folder
binwalk -e AGT.jpeg
We get some directory as Secret Stuff...->Don't Open This...->I Warned You .jpeg so we check this file also
with file command and
we get a data file. You can check this data file with either strings or xxd
strings return a text representation of file and xxd also shows hex dump
xxd I\ Warned\ You.jpeg
Now you search for flag or CTF using vim or any text editor and lucky you get one.