When adding elements from the Library to the Canvas, you have a couple options. Basically, when an element is added, it can either be treated as a Layer with properties, or simply an image you wish to use on the Canvas with no price affecting properties. Lets look at an example...

Lets imagine we want to add a Cake to my Design, as a Layer. We would open up the Library and click on one of the view icons for that Cake...

After the Cake is added to the Canvas, we would see the Cake as a Layer on the Layers Panel...

We can now add a Flavour to this cake through the Properties Panel and its price would be displayed on the Layer and on the Design Summary. We would also see the Servings displayed on the Servings Panel. 

Now lets imagine that we want to also show a side view of the Design, maybe to show how Construction would look within the Cake. If we were to add the Cake as a Layer again, Cakenote would treat the second Cake as an actual second Cake when in real life, there will only be one Cake. So the Servings Panel would display double the amount of Servings and if this item happened to have a default price (the Cake in this example doesn't), it would also be added to the Summary which would also cause the total price of the Design to be more than what it should be.

This is where the Image Only option becomes useful. Its used when you want to add anything from the Library, just for visual purposes and not for calculative purposes. To add an element as an Image Only layer, simply use the buttons below the view icons...

These buttons are blank until you move your cursor over them. Image Only layers will show up on the Layers Panel as a thin blank strip (purple if selected). This is so you can still understand where they are located in the arrangement (above or below other layers).