The software doesn't have a capture option which means you can't pause and take a still image of what you see to JPG format. However, you can use other applications that are developed to capture images from your screen.
Try installing GreenShot, an application that captures the desktop and what you see.
Download page: http://getgreenshot.org/
Once installed, play the file, pause it and then press one of the corresponding capture keys to take a screenshot.