In this work we propose the use of digital watermarks to establish track history of multiple tracked objects.
Target tracks extracted from a frame sequence can be represented and analyzed using spatio-temporal graphs.
However, this approach requires extensive computation and data storage. It is possible to achieve the same result
by digitally watermarking each tracked target. This self-contained video can then be searched to extract track
history. Track history is obtained by computing a quantity called target adjacency matrix. Interpretation of the
elements of this matrix, their location, magnitude and movement will establish desired track history. Given two
randomly selected frames we can establish changes of spatial relationship among targets in the two frames as
well as entry or exit of new targets in each frame.
Automatic tracking of targets in image sequences is an important capability. Although effective algorithms exist
to implement frame to frame registration, connecting the tracks across frames is of recent interest. The current
approach to this problem is by building a spatio-temporal graph. In this work we argue that the same rationale
used to fingerprint multimedia content for tracing purposes can be used to follow targets across frames. Riding
on top of a tracker, tracked targets receive unique watermarks which propagate throughout the video. These
watermarks can then be searched for and used in a newly defined target adjacency matrix. The properties of
this matrix establishes how target sequencing evolves across frames. The watermarked video is self-contained
and does not require buiding and maintaining of a spati-temporal graphs.