Over at http://homokaasu.org/rasterbator/
You’ll find the simple solution to this problem. You can either choose to make the image online or download a small app.Step one:
Select the number of A4 sheets the final image is going to cover.
Adjust the settings for the image.
Rasterbate the image. Save the produced pdf-file and print it.
Grab a pair of scissors and glue and paste the whole thing together
and you can see some fine examples of the images people have created with the app.