To set up a Déjà Vu image portfolio, the user selects a specific number of images from a larger set of images presented by a server. Figure 2 shows the image selection phase in our prototype.
The type of images used has a strong influence on the security of the system.
For example, if the system is based on photographs, it would be easy for users
to pick predictable portfolios, to describe their portfolio images and to write
down this information and share it with others. For this reason, we use Andrej
Bauer's Random Art to generate random abstract images [Bau98].
Given an initial seed, Random Art generates a random mathematical formula which
defines the color value for each pixel on the image plane. The image generation
process is deterministic and the image depends only on the initial seed. It is
therefore not necessary to store the images pixel-by-pixel, since the image can
be computed quickly from the seed. All images are hand-selected to ensure consistent quality.
Figure 1 illustrates sample Random Art images and appendix A discusses Random Art in more detail. Other methods exist for automatically synthesizing images [Sim91]. We did not explore these and leave this as an area for future study.
Figure 1: Examples of Random Art images
Figure 2: Portfolio selection window