My husband and I are planning a trip to the South of Spain in January. We are photographers. Can someone suggest which city would be best for our 7 day home base? We're planning to use a time-share so we won't be moving to different hotels.

I'd say Seville. It's the largest and has the most extraordinary collection of buildings in the old city, and it's lovely in winter as there are few tourists yet all the sights are open, and still oranges grow on the trees.
Makes a great base for touring nearby towns and cities like Córdoba, Cádiz, Jerez, Arcos, Ronda etc. It's a good 3-hour drive to Granada, and if possible try to stay a couple of nights there.

Cadiz often gets overlooked on this Forum, and would be reachable from Seville. I love Malaga and that could also be a base for Granada and Cordoba. I travelled to Seville from Malaga but it was a trek and I had to rush a wonderful City.

The south of Spain has been well-photographed, so it all depends what you are going to do with the photos.

I second Málaga or Sevilla, both are gret cities and very "photogenic".

300 year old Cádiz is special, also wonderful light. 90 mins from Sevilla by bus. http://www.youtube.com/watch?v=g84pEehRgm0

Small Ardales, a little north of Málaga city. http://www.youtube.com/watch?v=3ivhFNtA1RU