We are given a file with ASCII letters. Searching for "APERTURE IMAGE FORMAT (c) 1985" on Google, we find out that it is a specific file format used in Portal (http://portalwiki.asshatter.org/index.php/Aperture_Image_Format.html). I downloaded one of the Windows Binaries from the website (Method 1) and swapped out the APF file with the file given, but the image did not load.
I compared the original APF file with the mayday file and noticed that the original file did not include the 2nd and 3rd line. I deleted them ran the executable again, which successfully resulted in the message "THE SHIP IS STOLEN"
Flag: vsctf{THESHIPISSTOLEN}