Unlike the Windows version, the Mac version of Skype doesn't include a snapshot feature. You can use the Mac OS X built-in app "Grab" which is what other people are recommending with the key combinations (imho). It will save a fullscreen, window, or selection to a TIFF file, which you can then re-open in Preview and save it as something else if you so desire.
so what? beacause mac has the opportunity to take screenshots the skype doesnt give you the chance to take a picture of your friend? I cant understand it !! I also have a mac and this was my question .. Skype please make a new skype version for mac and give us the chance to take picture of our friends normally from skype and not from the mac!
also after you do CMD + Shift + 4
you can then press space bar.. and the crosshair will convert to a camera that will size a perfect cut for the window of your choice