1. Download cafeteria photo from CTF website.

2. Crop logo on the glass. (I did it by gimp)

3. Search for logo in Google images. You can see the result here.

4. It will find this photo. Go to root directory of that website and download all photos in that directory.

5. Check EXIF data of all images by ExifTool:

exiftool logo_6a47d39b77f1b182147fa51fe444ac58.png

6. in this line you see nickname of image creator:

Comment                         : Designed by: nooneonemore.For: http://suctf.com/cce1/d393.

7. Make md5sum by this command in GNU/Linux shell:

echo -n "nooneonemore" | md5sum