We are given a challenge.zip that has a directory home with the following directory tree:

$ tree -a .
.
└── ctf-player
    └── drop-in
        └── flag.png

3 directories, 1 file

Viewing flag.png is a QR code image.

I use the zbarimg tool, used to read QR codes from images. I use it in my terminal and get the flag:

$ zbarimg ctf-player/drop-in/flag.png
QR-Code:picoCTF{p33k_@_b00_3f7cf1ae}
scanned 1 barcode symbols from 1 images in 0.01 seconds

Flag: picoCTF{p33k_@_b00_3f7cf1ae}

Note: This could also be solved scanning manually with a mobile device or using an online website to do so!