The 'Add Image' function on Symphony is different depending on whether you are the customer modifying the product (Figure 1) or the administrator creating the product (Figure 2)

(Figure 1: Front-End)

As a customer modifying the product you can insert images from your albums stored in My Account > Album Management or by copying the image URL into the field at the top of the popup

(Figure 2: Back-End)

If you are creating the product then images will need to be added via URL only. The best way to do this would be to upload images to your storefront through Catfish > Email > Email Resource Upload (Figure 3)

(Figure 3: Image Upload)

Once you have selected and uploaded your file right-click and copy the image address (Internet Explorer - Copy Shortcut, Firefox - Copy Image Location) and paste this into the Add Image via URL field. Click Ok and the editor will fetch the image to display on your product