This challenge was a fun relaxing one, playing around in GIMP and eventually discovering a new tool which looks useful for future stego challenges.
My first intuition was to go into GIMP and start playing around with threshold, color balance and curves.
Out of that I got a partial reveal of the Flag:
After taking a break and coming back, I decided to research what other people were doing to solve CTF stego challenges out there.
I stumbled upon Balda's Stegpy Release page -
http://www.balda.ch/posts/2013/Jun/04/release-stegpy/
Github link - https://github.com/Baldanos/Stegpy
After playing around with this tool (Which was very nice to use), I found the flag within seconds:
$ python stegpy.py -V castle.png
