Just above the preview window, near the right side of the row of icons, is an icon that looks like two pieces of paper overlaid on top of each other. Hover over it with your mouse and it should say "Copy Snapshot to Clipboard." Click on that. For best results, set the preview quality to "Best" before taking the snapshot.
If you do a lot of this, there is a script that temporarily changes all the settings to their optimimum values so that you get the best possible resolution, and handle the deinterlacing issues correctly. You can download this script, along with others at: