Plastic Who,
Select the image, click copy on the formatting toolbar, go to the other
presentation (click on the taskbar of Windows or press CTRL+F6 to switch) -
click on the paste button.
Or open the two presentations, go to Windows menu, choose all windows.
Select the image, hold down the ctrl key and drag it to the other
presentation slide. First release your left mousebutton then the ctrl-key.
Does that help?