Typically looks like CTF{...} or FLAG{...} .
Looking for a in the archive (using 7z l -slt Bach_Guitar.rar ). Bach_Guitar.rar
Use strings to look for readable text at the end of the file. Inspect the LSB (Least Significant Bit) using zsteg . Open the file in Audacity . Typically looks like CTF{
A text file named flag.txt extracted from the image. Bach_Guitar.rar