I take it you added the img tag to the list of allowed HTML? You will also have to add the width, height, and src attributes as allowed attributes to the img tag.
In the Configuration, click on the (+) button behind the img tag (in the same line), then use "Add Element" to add the required attributes.
As of Geeklog 1.6.0 this is all done automatically (again) when you enable FCKeditor - that was a bug in 1.5.x.
bye, Dirk