Nice. a video game pixel art take on github profile art. I first saw a proof of concept on Will Leinweber's profile ( https://github.com/will/ ) The downside is the top place in your 'Contributions' feed gets heavily polluted..
It's a Python script that takes in some options (which image, your github username, etc) and generates a bash script. Running the bash script actually makes the commits on the correct days to populate the pixels.
luckily git takes both GIT_AUTHOR_DATE and GIT_COMMITTER_DATE as environment variables. This python script generates a bash script that sets a date and commit one line changes for every pixel that needs some gitfiti.
And the write-up: http://kivikakk.ee/2013/05/07/contrigraph.html