You can adjust the error tolerance, for instance if you want to be able to put a Bitcoin logo in it.
The man page isn't that long.
From my cheat sheet:
qrencode -t png -o file.png -s 10 'private key here'
# Make QR code with 25% error tolerance (preferred option!)
qrencode -t png -o file.png -s 10 -l Q 'private key here'
# Make QR code with 30% error tolerance
qrencode -t png -o file.png -s 10 -l H 'private key here'
Example with 25% error tolerance used for the logo: