I think I can help you with this one. For my pictures, I use a regular chair and then stick to it a large sheet of white Bristol Board
I set one (or two) pieces on a chair and then place the MOC on top. All my pictures are taken outside, in natural light, but never in straight sunlight as the sun will create shadows.
After I take the pic, I will adjust the brightness (this is very minimal adjusting) and crop the photo in an program called Picasa
Finally I will edit out the parts of the photo that still show some of the house siding, or chair. These are usually in the corners. Which reminds me that all you have to make sure is that their is a white border all around the photo then you wont have to worry about erasing part of your MOC.
I use Paint
and just select the colour of the background and fill it in with a paintbrush.
The picture goes from this:
NOTE: (The two photos above are actually not the same but I just wanted to show an unedited version so you can see the chair/house in the background)
This is the easiest way in my opinion as all you need is a chair, white Bristol board, and your MOC.
Also AK_Brickster has a helpful tutorial/advice
if your into using GIMP.
Hope this helps some!