I'm not sure if I'm on the same page as everybody else here.
I've loaded the images from the SD card onto the laptop. Then I've plugged in the external hard drive and transferred them over. So with them on the Western Digital thing I don't see why I need to keep them on the laptop, therefore, I disconnected the hard drive and deleted them from the laptop.
But, when I plugged the WD thing back in, the images I'd deleted from the laptop had gone from the WD thing as well. Seeing as they weren't connected at the time of deletion I don't understand how they can go from both devices.
I'm not actually interested in getting images back as apart from one or two, I've only deleted the pictures I didn't want, but it might be an idea to get rid of all the ones I've transferred.