"Alpha Blend" is the seventh piece in the Shadow Box series of interactive displays with a built-in computerized tracking system. This piece shows the viewer's presence revealing and blending pictures of people who have recently looked at the work. A game of "reverse puppetry" ensues, where a portrait from the past is animated by a live presence, in a similar preceptual mechanism than the one used in Lozano-Hemmer's public art installation "Body Movies". Half the time an immediately previous image is shown while the other half of the time an image is selected at random from up to 10 years of recordings.