an electronic screen capable of showing dynamic images is used to display a set of barcodes , where the barcodes are ‘ played ’ at the same location on the screen . the screen might also show other material . the data encoded in the barcodes is decoded by a user with a cellphone and camera , that can decode each barcode and combine the data from all the barcodes . this can be extended with the screen also showing static barcodes that encode urls , where the urls go back to a web server that also controls the screen . a user with a cellphone and camera scans one of these static barcodes and uses a browser to go to the decoded url . the web server uses this visit to change what is being shown in the dynamic barcodes , or to change the conditions under which the latter are displayed .