Coffee spill obliterate part of that important letter? All you need is a paper towel and some cryptographic digital-signature technology from Palo Alto Research Center in Palo Alto, CA. Then you can clean up the mess and reconstruct the full page-words and images alike-in seconds. The technology, which PARC is seeking to license, starts by encoding the original document in a series of slashes-each just one-half millimeter across-that represent ones and zeroes. These “glyphs” may be printed as an unobtrusive gray screen on the back of the original. Scanning any 75 percent of a document’s gray screen gives a computer all the information it needs to rebuild the original. The key to this process is image compression technology that can render images with a minimum of glyphs, as well as redundancy within the glyphs and error correction software that fills in missing data. “Just as the Internet can recover from packet loss; we can recover from page loss,” says Jeff Breidenbach, the system’s developer.