Using USB Webcam on Mac with build-in iSight
For Sparkbooth 3.5 or later, there should no issue with using a USB webcam. Press F3 to display camera settings, and select the webcam from the camera list. If the video is stretched or too narrow, use the Scale Width slider in the camera settings to adjust.
For Sparkbooth 3.4 or earlier, please update to Adobe AIR 3.1 or later which will allow you to select from multiple webcams on Macs. You can download the latest Adobe Air at http://get.adobe.com/air. If you still only see "Default Camera", go to Settings > Options tab > Other from drop down list > Uncheck "Use default camera only"