I am currently on a Mac OS X 10.7.5 using Audacity 2.0.3
When I attempt to use the screenshot tool to capture a track image, all I get is a black png file as the output. I understand that I can use the screenshot tool for the Mac OS, but wanted to use the the one that comes with the program.
In the mean time, you can use the two Mac screen grab tools: Command-Shift-3 will capture the whole screen and Command-Shift-4 will allow you to draw a box around the portion of the screen you want included in the capture.