Both of these are examples of “crowdsourcing” which means to involve the viewer and to generate a piece of artwork created by a large number of people from all over the world. The first link is to a project by Aaron Koblin and Chris Milk that required the audience to create a single animated frame which when combined created a music video for Johnny Cash’s final song “Aint No Grave”.
The second link, by the same two artists, is a digital picture of a $100 dollar bill which was created in 10,000 different pieces by people from all over the world.
These are really good examples of online work being created by a huge number of people getting involved. Im not sure how the artists made sure enough people got involved.