As far as I know importing pictures INTO the actual cell cannot be done…at least not easily. You may want to check out some information on VB scripting in Excel to answer this one…but, like I said, putting a picture into a cell. You can place pictures OVER cells.
When you create a drop down menu, you are essentially making another column of cells, that just isn’t visible constantly. Because of this, they tend to carry the same functions as regular cells, only a bit more. With this in mind, I doubt their ability to contact graphics.