How to add an image to an item?

Under view mode, click on the item you wish to add an image, once you click the name of the Item you wilsh to update, a pop-up page will appear and at the bottom of that page, there are 3 shaded options, and one of them is "Update Image", just click on that and an "Edit Item Image" page will appear. 

There are 3 ways to add an image and the easiest way would be 'URL'. 

Click on URL and an "Image URL" box will show up and you can paste an image address copied from any source. After adding the image address, the image will show up to check if you have added the right image. Just click "Save Image" to complete the Update.