I found a photograph I liked for my living room and downloaded the free software Rasterbator. After unpacking the downloaded zip-file, the software is ready to use and comes with a readme file with some explanation.
When starting the program, you can choose your language, image, paper size and number of tiles. It will also show you how large your poster will become at that point.
As it turned out, to get not just some random dots on a sheet of paper, I had to set the dot size to 1mm. This makes the software very sluggish, but the output will be better.
And don't forget to select the option Multi Color at step 4! (Unless you want a black and white image of course.)
After Rasterbator does it's thing, you will have a pdf-file you can print.
Last tip: get some extra printer cartridges and paper as these things tend to go wrong first time round and the prints use a lot of ink.
I decided to keep some space between the prints to accent the tile character.
All in all, I like the result!