Well... a synth isn't a single image. Are you talking about getting a picture of your synth in action (taking a screenshot of part of it) or saving the whole thing offline?
If all you want is a screenshot, the 'Print Screen' key and pasting into Paint or another photo editor should solve your problem.
If, on the other hand, what you really want is to save and view your synth offline, this is not supported. I can tell you how to copy the files for a synth, but I don't have a way of viewing them once I've got them offline so it doesn't do a great deal of good.
If you want to read anyway, click here: http://getsatisfaction.com/livelabs/topics/can_a_synth_project_be_burned_to_disc#reply_1237626