What you have done is merely create a property that stores a value in a variable that Visual Studio implicitly created. You stored value then goes no where, therefore does nothing.
I think what you are trying to do is fill you ImageDisplayByValue with your images from the ImageList. To do this, simply set the ImageSize property of your ImageList to the same dimensions as the Size property of your ImageDisplayByValue.
In other words get the Size of your ImageDisplayByValue, then select the ImageList and copy that size into the ImageSize property.