Problem Statement
I bet your eye can spot the original photo!
So, we're provided with a zip file images.zip. Let's unzip it and see.
$ unzip images.zip -d data/
Archive: images.zip
inflating: data/0001.png
inflating: data/0002.png
...
inflating: data/1154.png
These are a lot of images! Looking normally through some photos, all looked same. I checked more and observed that each image has somewhat similar part at end of it which is
DCTF
%tEXtCopyright
trololololololololololololo
%tEXtdate:create
2017-09-29T13:30:00+03:00c6&
%tEXtdate:modify
2017-09-29T13:30:00+03:00
tEXtSoftware
Shutterc
IEND
Focussing more on problem statement, there's an odd-one out image. So, lets see data of all images and try to grep for flag.
$ grep -H "DCTF{" data/*
Binary file data/1024.png matches
$ strings data/1024.png | grep "DCTF{"
DCTF{162d6e3865b2be32851fb8bd3cca73bdc1a052f9da75d8680c471eb45af522df}
Flag: DCTF{162d6e3865b2be32851fb8bd3cca73bdc1a052f9da75d8680c471eb45af522df}