I looked all around this website, and as far as affiliation with the Church or Catholic organizations, it seems to be supported by the Diocese of Cologne, the WYD people, and these guys, which seem to be a website for (a? the?) cathedrals of Cologne. So there's the disclaimer! "Late Pope John Paul II is the grand-father of the World Youth Day (WJT). It was him, who – in 1984 - initiated the first world meeting of young people in Rome. His idea: Every two years, the Pope invites young people from all over the world to come to one town to experience Christ and his living church.
We want to say thank you to the inventor of the World Youth Day: By means of the biggest mosaic portrait the world has ever seen. To accomplish this, we need your photograph. From thousands of portrait photographs, your portraits, we will build an image of late Pope JP II."
Go take a look! This should be an English link (the site is in frames). If it is not English, click the british flag on the top right-hand side! I'll edit this tonight so I can put the picture in of the poster :).