In an effort to keep corporations and businesses from using Google Author, Google apparently is scanning Google Author images to verify whether they look like recognizable headshots (where the face can easily be seen).
The full-body shot (see images to the right) that I posted to my Google profile was showing up in Google Author for several weeks, but then it inexplicably disappeared.
When I substituted the second image that you see on the right (a more-recognizable headshot), this second image began to appear (a few days later) in keyword searches.
The moral of the story, apparently, is to make sure that you post a headshot, and not a full-body or mid-body photograph, to your Google profile so that it will come up in keyword searches.
Also, be sure that your profile headshot is at least 300 pixels by 300 pixels.