TSGCTF 2020 Poor Stego Guy Writeup

The key point is that noise.jpg is saved with the option -quality 50. Low-quality jpeg images have very small representation space, and thus the representation space is sparse. So, images that are very close to noise.jpg are likely to be exactly same as noise.jpg after jpeg compression.

We have output.png, which is very close to deleted noise.jpg.

docker run -v `pwd`:/mnt dpokidov/imagemagick:7.0.10-9 /mnt/output.png -quality 50 /mnt/noise.jpg

We get noise.jpg.

TSGCTF{YoU_aR3_tHe_4b5oLuTe_w1nNer_of_JPEG!}