For anybody that has ever wondered how screenshots can be taken on a Garmin GPS you will be pleased to know that it is actually a built in function and all you need to do is follow this guide to enabling and taking screenshots on Garmin NUVI devices.
All you need to to do is enable to feature by visiting tools (the spanner), display and turning on the screenshot option as seen below.
This will allow you to take screenshots on your garmin device, the files are saved to Drive:\Garmin\scrn with Drive being the letter assigned to your garmin when you plug it into your computer with the usb cable.
Once enabled you will notice a camera icon floating around the GPS screen. Tapping this icon will take a screenshot. The icon disappears if the Garmin is restarted.
You can take screenshots in any view and they come out perfectly in 3D or 2D modes.
By Default Garmin saves the files at BMP which can take up a fair amount of space so if your device is low on space be sure to remove the screenshots often.