We made use of one property of the JPEG file structure:

> "If a 0xff byte occurs in the compressed image data either a zero byte (0x00) or a marker identifier follows it. Normally the only marker that should be found once the image data is started is an EOI. When a 0xff byte is found followed by a zero byte (0x00) the zero byte must be discarded."

More details on the original writeup.

Original writeup (https://github.com/kral-ctf-team/writeups/blob/master/2017/seccon-2017-online-ctf/JPEG-file.md).