Figure 3.
STEP 1 :-
First you must bring the LAYERS box onto your screen so click the WINDOW Toolbar at the top of the screen and then click LAYERS which should be the 9th one down on the list (I am using Photoshop CS). Personally I use the Keyboard shortcut for this which is the Function key F7.
Once the LAYERS BOX is on screen click the small arrow that points to the right as indicated in my STEP 1 diagram, this will bring out a list of options and go to DUPLICATE LAYER then click your left Mouse button.
STEP 2 :-
As soon as you click the left Mouse button a new box will appear on screen as seen in the STEP 2 so all you need do next is to click OK.
STEP 3 :-
Once OK is clicked it will create a BACKGROUND COPY in the LAYERS box as shown in STEP 3.
Those are the steps to create a DUPLICATE LAYER and once this has been completed you can remove the LAYERS box from the screen by click the red X (also shown in my STEP 3 diagram), it does not require to be displayed and if it is left there it get's in the way for working on the photo.
I always shoot with my Canon 10D in RAW mode rather than using JPEGS and after completing my scan in Photoshop I save them as Tiffs.
One of the good things about DUPLICATE LAYER is that if it is saved as a TIFF for future use you can open up the scan later and the DUPLICATE LAYER will still be there, the BITMAP and JPEG Formats will not save the duplicate layer in effect it is FLATTENED so you would have to duplicate the same steps again as described above.