参考：
http://blog.squareroots.de/en/2015/10/asis-ctf-finals-2015-strange/
After extracting we noticed that the file has dimensions of 344987×344987 pixels. OK that is huge! Since there was no preview of the picture generated, which would indicate a normal picture with something attached after the picture
文件太大，用Mac自带的图片查看应用打不开，而且没有预览，于是猜想可能是有一张普通的图片然后在其后夹杂着其他的东西。
用010 Editor也打不开
按照这篇文章
https://kt.pe/blog/2015/10/asis-2015-finals-strange/
说的，
We got a PNG file with a size of 15MB.
You cannot open the file as some programs simply freeze, others show out of memory exceptions, or other errors.
然后它提到说可以用Wireshark打开啊。
可以看到它的一些基本信息，比如width和height。
然后发现其中充斥着大量的000000000000
看writeup都看不懂还是放弃了。