This can be done in an interesting way. First, go to the cell you want the picture to appear in. Then, hit Shift+F2 to create a comment box.
Right click on the box and choose "Format Comment", then choose the "Colors and Lines" tab.
Under "Fill" go the "Color" pull down and select "Fill Effects" all the way at the bottom.
Then choose the rightmost tab "Picture" and insert your saved pic. Select "Lock picture aspect ratio" at the bottom as well.
Now everytime you mouse over the cell, the comment box will open with your pic in it.