My thanks to all who commented.
The image of Wilt was originally part of the limited edition glicee print that I bought years ago. Extracting him from the background was an interesting experience at the time, considering that I had no idea what I was doing; the "one pixel at a time" method works and produces a nice smooth edge but with an image that size (about 3200 pixels tall) it can be a tad time-consuming. Makes for a very nice desktop pic, too.