1) To ensure that you get the best quality, click the photo so that lightbox opens the image.
2) Right-click the image so that the context menu appears:
Firefox: Select "Set as Desktop Background..." and choose from the position options as below (Center or Fit will generally provide the best look).
|Options from Firefox|
Internet Explorer: Select "Set as Background". To change position settings you will need to set the personalise settings for the desktop in Control Panel:
|Control Panel settings|
Chrome: Command click on photo (above); it opens in a new Tab. Drag to desktop. Use "Desktop & Screensaver" in System Preferences to center and choose background color.
To Hollis, over at In the Company of Plants and Rocks, for the Mac instructions.
To Jessica Burke from Moss Plants and More for such the idea.
Note: If anyone uses other Operating Systems and could let me know the instructions for applying the photo as a desktop image, please get in touch!