Methods and apparatus, including computer program products, for transmitting content from a content collection site to a content monitoring site, including inserting a first digital signature into a first content segment collected by the content collection device, inserting a second digital signature, different form the first digital signature, into a second content segment collected by the content collection device sequentially after the first content segment, and transmitting the first content segment including the first digital signature and the second content segment including the second digital signature to the content monitoring site.