You can do this without the use of a secondary program. Follow these steps:
- Set your game to Windowed mode
- Have another program open, like Calculator
- Switch to Calculator and drag the program window to the bottom corner of your desktop to get it out of the screenshot
- Switch back to GW2 and hover your mouse over the item in question
- Alt+tab back to Calculator and do not move your mouse
- Hit the Print Screen button
- Open up Paint and paste
Essentially what this does is take a screenshot of your current windows desktop, which just happens to have GW2 in the frame. You will need to crop your start bar out of the picture, but it's a way to get what you're after without the need to install additional programs.