There are two ways I would suggest: one digital; one manual.
Digital you will need to start with a color photo. There are different techniques. I love Picasa which is free to download from Microsoft. It's even better than may of the products I've purchased.
Manually you can use ink and a plastic tip. You just color in the areas use wish. Recollections and Michaels carry the Tim Holtz inks (Adirondack), tips and instruction manuals. This technique adds the antique look, which is less stark than using actual markers.
Have fun!