I don't have the Magix Rescue program, but their other video editors (MEP & VPX etc) have the ability to export the current frame as either a JPEG or BMP image file. The option is however 'hidden' under the 'File' >> 'Exportmovie' menu and might easily be missed. You should be able to pick a pixel resolution different from the current project but there is little sense in in making an enlargement. I use the option to create small stills (640x360) from HD video (1920x1080).
If all else fails you can always do a Windows screen capture, [Print Screen] key, of your program preview and crop if necessary.